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 $104.37   13.201%   $118.1479   $118.15   $118.15   $118.10  
  Purchase #2 $23.54   8.423%   $25.5228   $25.52   $25.50   $25.50  
  Purchase #3 $97.88   11.821%   $109.4504   $109.45   $109.45   $109.50  
  Purchase #4 $185.69   4.838%   $194.6737   $194.67   $194.65   $194.70  
  Purchase #5 $126.28   7.615%   $135.8962   $135.90   $135.90   $135.90  
  Purchase #6 $141.92   7.307%   $152.2901   $152.29   $152.30   $152.30  
  Purchase #7 $226.73   8.809%   $246.7026   $246.70   $246.70   $246.70  
  7 purchase totals = $906.41       $982.6837   $982.68   $982.65   $982.70