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 $213.70   6.231%   $227.0156   $227.02   $227.00   $227.00  
  Purchase #2 $58.98   5.662%   $62.3194   $62.32   $62.30   $62.30  
  Purchase #3 $93.86   9.686%   $102.9513   $102.95   $102.95   $103.00  
  Purchase #4 $243.86   9.432%   $266.8609   $266.86   $266.85   $266.90  
  Purchase #5 $203.96   4.454%   $213.0444   $213.04   $213.05   $213.00  
  Purchase #6 $226.34   3.748%   $234.8232   $234.82   $234.80   $234.80  
  Purchase #7 $194.46   9.758%   $213.4354   $213.44   $213.45   $213.40  
  7 purchase totals = $1,235.16       $1,320.4502   $1,320.45   $1,320.40   $1,320.40