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 $222.46   8.449%   $241.2556   $241.26   $241.25   $241.30  
  Purchase #2 $204.53   10.698%   $226.4106   $226.41   $226.40   $226.40  
  Purchase #3 $50.90   6.120%   $54.0151   $54.02   $54.00   $54.00  
  Purchase #4 $185.40   4.771%   $194.2454   $194.25   $194.25   $194.20  
  Purchase #5 $162.92   4.663%   $170.517   $170.52   $170.50   $170.50  
  Purchase #6 $67.91   6.650%   $72.426   $72.43   $72.45   $72.40  
  Purchase #7 $25.44   11.207%   $28.2911   $28.29   $28.30   $28.30  
  7 purchase totals = $919.56       $987.1608   $987.18   $987.15   $987.10