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 $43.30   6.252%   $46.0071   $46.01   $46.00   $46.00  
  Purchase #2 $139.35   11.618%   $155.5397   $155.54   $155.55   $155.50  
  Purchase #3 $81.73   8.419%   $88.6108   $88.61   $88.60   $88.60  
  Purchase #4 $65.26   6.163%   $69.282   $69.28   $69.30   $69.30  
  Purchase #5 $118.44   6.810%   $126.5058   $126.51   $126.50   $126.50  
  Purchase #6 $247.29   5.453%   $260.7747   $260.77   $260.75   $260.80  
  Purchase #7 $234.29   3.671%   $242.8908   $242.89   $242.90   $242.90  
  7 purchase totals = $929.66       $989.6109   $989.61   $989.60   $989.60