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 $37.34   7.563%   $40.164   $40.16   $40.15   $40.20  
  Purchase #2 $224.31   7.604%   $241.3665   $241.37   $241.35   $241.40  
  Purchase #3 $62.68   8.745%   $68.1614   $68.16   $68.15   $68.20  
  Purchase #4 $165.51   13.647%   $188.0971   $188.10   $188.10   $188.10  
  Purchase #5 $138.71   7.717%   $149.4143   $149.41   $149.40   $149.40  
  Purchase #6 $136.41   10.770%   $151.1014   $151.10   $151.10   $151.10  
  Purchase #7 $109.74   13.374%   $124.4166   $124.42   $124.40   $124.40  
  7 purchase totals = $874.70       $962.7213   $962.72   $962.65   $962.80