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 $226.36   8.679%   $246.0058   $246.01   $246.00   $246.00  
  Purchase #2 $148.81   11.570%   $166.0273   $166.03   $166.05   $166.00  
  Purchase #3 $127.90   6.540%   $136.2647   $136.26   $136.25   $136.30  
  Purchase #4 $97.65   4.223%   $101.7738   $101.77   $101.75   $101.80  
  Purchase #5 $188.93   7.588%   $203.266   $203.27   $203.25   $203.30  
  Purchase #6 $24.33   10.814%   $26.961   $26.96   $26.95   $27.00  
  Purchase #7 $37.45   12.703%   $42.2073   $42.21   $42.20   $42.20  
  7 purchase totals = $851.43       $922.5059   $922.51   $922.45   $922.60