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 $80.41   10.201%   $88.6126   $88.61   $88.60   $88.60  
  Purchase #2 $52.38   12.140%   $58.7389   $58.74   $58.75   $58.70  
  Purchase #3 $131.74   13.446%   $149.4538   $149.45   $149.45   $149.50  
  Purchase #4 $76.98   10.400%   $84.9859   $84.99   $85.00   $85.00  
  Purchase #5 $232.92   9.316%   $254.6188   $254.62   $254.60   $254.60  
  Purchase #6 $99.39   5.598%   $104.9539   $104.95   $104.95   $105.00  
  Purchase #7 $34.41   9.446%   $37.6604   $37.66   $37.65   $37.70  
  7 purchase totals = $708.23       $779.0243   $779.02   $779.00   $779.10