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 $183.69   10.313%   $202.6339   $202.63   $202.65   $202.60  
  Purchase #2 $236.69   13.187%   $267.9023   $267.90   $267.90   $267.90  
  Purchase #3 $48.67   4.554%   $50.8864   $50.89   $50.90   $50.90  
  Purchase #4 $137.46   5.163%   $144.5571   $144.56   $144.55   $144.60  
  Purchase #5 $104.51   6.455%   $111.2561   $111.26   $111.25   $111.30  
  Purchase #6 $47.32   5.762%   $50.0466   $50.05   $50.05   $50.00  
  Purchase #7 $232.62   3.614%   $241.0269   $241.03   $241.05   $241.00  
  7 purchase totals = $990.96       $1,068.3093   $1,068.32   $1,068.35   $1,068.30