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 $47.41   3.244%   $48.948   $48.95   $48.95   $48.90  
  Purchase #2 $140.56   11.862%   $157.2332   $157.23   $157.25   $157.20  
  Purchase #3 $118.57   6.587%   $126.3802   $126.38   $126.40   $126.40  
  Purchase #4 $105.56   9.838%   $115.945   $115.95   $115.95   $115.90  
  Purchase #5 $219.87   10.802%   $243.6204   $243.62   $243.60   $243.60  
  Purchase #6 $99.82   9.222%   $109.0254   $109.03   $109.05   $109.00  
  Purchase #7 $104.41   12.747%   $117.7191   $117.72   $117.70   $117.70  
  7 purchase totals = $836.20       $918.8713   $918.88   $918.90   $918.70