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 $51.46   12.648%   $57.9687   $57.97   $57.95   $58.00  
  Purchase #2 $207.55   6.403%   $220.8394   $220.84   $220.85   $220.80  
  Purchase #3 $120.89   9.511%   $132.3878   $132.39   $132.40   $132.40  
  Purchase #4 $56.66   11.190%   $63.0003   $63.00   $63.00   $63.00  
  Purchase #5 $63.85   3.152%   $65.8626   $65.86   $65.85   $65.90  
  Purchase #6 $113.97   5.533%   $120.276   $120.28   $120.30   $120.30  
  Purchase #7 $125.72   12.215%   $141.0767   $141.08   $141.10   $141.10  
  7 purchase totals = $740.10       $801.4115   $801.42   $801.45   $801.50