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 $210.66   6.345%   $224.0264   $224.03   $224.05   $224.00  
  Purchase #2 $88.98   5.160%   $93.5714   $93.57   $93.55   $93.60  
  Purchase #3 $221.71   3.520%   $229.5142   $229.51   $229.50   $229.50  
  Purchase #4 $94.39   9.853%   $103.6902   $103.69   $103.70   $103.70  
  Purchase #5 $79.62   9.524%   $87.203   $87.20   $87.20   $87.20  
  Purchase #6 $73.42   11.533%   $81.8875   $81.89   $81.90   $81.90  
  Purchase #7 $48.51   9.462%   $53.1   $53.10   $53.10   $53.10  
  7 purchase totals = $817.29       $872.9927   $872.99   $873.00   $873.00