Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $227.31   6.201%   $241.4055   $241.41   $241.40   $241.40  
  Purchase #2 $221.29   9.614%   $242.5648   $242.56   $242.55   $242.60  
  Purchase #3 $137.54   12.395%   $154.5881   $154.59   $154.60   $154.60  
  Purchase #4 $245.32   11.406%   $273.3012   $273.30   $273.30   $273.30  
  Purchase #5 $207.93   4.681%   $217.6632   $217.66   $217.65   $217.70  
  Purchase #6 $153.36   6.780%   $163.7578   $163.76   $163.75   $163.80  
  Purchase #7 $194.38   5.216%   $204.5189   $204.52   $204.50   $204.50  
  7 purchase totals = $1,387.13       $1,497.7995   $1,497.80   $1,497.75   $1,497.90