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 $104.58   8.219%   $113.1754   $113.18   $113.20   $113.20  
  Purchase #2 $113.96   5.168%   $119.8495   $119.85   $119.85   $119.80  
  Purchase #3 $200.44   7.736%   $215.946   $215.95   $215.95   $215.90  
  Purchase #4 $236.75   7.714%   $255.0129   $255.01   $255.00   $255.00  
  Purchase #5 $117.42   4.495%   $122.698   $122.70   $122.70   $122.70  
  Purchase #6 $82.50   3.408%   $85.3116   $85.31   $85.30   $85.30  
  Purchase #7 $101.73   10.170%   $112.0759   $112.08   $112.10   $112.10  
  7 purchase totals = $957.38       $1,024.0693   $1,024.08   $1,024.10   $1,024.00