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 $226.96   11.162%   $252.2933   $252.29   $252.30   $252.30  
  Purchase #2 $31.66   13.853%   $36.0459   $36.05   $36.05   $36.00  
  Purchase #3 $160.71   13.630%   $182.6148   $182.61   $182.60   $182.60  
  Purchase #4 $54.63   13.826%   $62.1831   $62.18   $62.20   $62.20  
  Purchase #5 $222.30   5.761%   $235.1067   $235.11   $235.10   $235.10  
  Purchase #6 $34.34   13.666%   $39.0329   $39.03   $39.05   $39.00  
  Purchase #7 $130.42   10.818%   $144.5288   $144.53   $144.55   $144.50  
  7 purchase totals = $861.02       $951.8055   $951.80   $951.85   $951.70