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 $43.94   10.661%   $48.6244   $48.62   $48.60   $48.60  
  Purchase #2 $119.66   9.761%   $131.34   $131.34   $131.35   $131.30  
  Purchase #3 $12.31   7.399%   $13.2208   $13.22   $13.20   $13.20  
  Purchase #4 $51.47   5.149%   $54.1202   $54.12   $54.10   $54.10  
  Purchase #5 $206.44   8.374%   $223.7273   $223.73   $223.75   $223.70  
  Purchase #6 $103.89   12.828%   $117.217   $117.22   $117.20   $117.20  
  Purchase #7 $43.54   8.189%   $47.1055   $47.11   $47.10   $47.10  
  7 purchase totals = $581.25       $635.3552   $635.36   $635.30   $635.20