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 $235.84   6.370%   $250.863   $250.86   $250.85   $250.90  
  Purchase #2 $58.75   4.388%   $61.328   $61.33   $61.35   $61.30  
  Purchase #3 $18.73   4.818%   $19.6324   $19.63   $19.65   $19.60  
  Purchase #4 $95.67   5.522%   $100.9529   $100.95   $100.95   $101.00  
  Purchase #5 $180.64   7.822%   $194.7697   $194.77   $194.75   $194.80  
  Purchase #6 $211.32   8.519%   $229.3224   $229.32   $229.30   $229.30  
  Purchase #7 $62.79   8.492%   $68.1221   $68.12   $68.10   $68.10  
  7 purchase totals = $863.74       $924.9905   $924.98   $924.95   $925.00