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 $184.39   13.749%   $209.7418   $209.74   $209.75   $209.70  
  Purchase #2 $151.38   13.399%   $171.6634   $171.66   $171.65   $171.70  
  Purchase #3 $98.43   4.273%   $102.6359   $102.64   $102.65   $102.60  
  Purchase #4 $158.50   3.638%   $164.2662   $164.27   $164.25   $164.30  
  Purchase #5 $157.33   11.730%   $175.7848   $175.78   $175.80   $175.80  
  Purchase #6 $10.29   10.454%   $11.3657   $11.37   $11.35   $11.40  
  Purchase #7 $118.49   3.478%   $122.6111   $122.61   $122.60   $122.60  
  7 purchase totals = $878.81       $958.0689   $958.07   $958.05   $958.10