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 $60.29   6.215%   $64.037   $64.04   $64.05   $64.00  
  Purchase #2 $196.82   5.297%   $207.2456   $207.25   $207.25   $207.20  
  Purchase #3 $169.34   8.646%   $183.9811   $183.98   $184.00   $184.00  
  Purchase #4 $110.31   6.731%   $117.735   $117.74   $117.75   $117.70  
  Purchase #5 $180.66   3.185%   $186.414   $186.41   $186.40   $186.40  
  Purchase #6 $151.74   9.579%   $166.2752   $166.28   $166.30   $166.30  
  Purchase #7 $142.82   7.639%   $153.73   $153.73   $153.75   $153.70  
  7 purchase totals = $1,011.98       $1,079.4179   $1,079.43   $1,079.50   $1,079.30