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 $85.80   8.228%   $92.8596   $92.86   $92.85   $92.90  
  Purchase #2 $120.69   11.632%   $134.7287   $134.73   $134.75   $134.70  
  Purchase #3 $99.53   8.866%   $108.3543   $108.35   $108.35   $108.40  
  Purchase #4 $174.91   6.849%   $186.8896   $186.89   $186.90   $186.90  
  Purchase #5 $179.90   6.458%   $191.5179   $191.52   $191.50   $191.50  
  Purchase #6 $237.61   3.852%   $246.7627   $246.76   $246.75   $246.80  
  Purchase #7 $100.49   9.659%   $110.1963   $110.20   $110.20   $110.20  
  7 purchase totals = $998.93       $1,071.3091   $1,071.31   $1,071.30   $1,071.40