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 $60.50   13.292%   $68.5417   $68.54   $68.55   $68.50  
  Purchase #2 $87.91   5.268%   $92.5411   $92.54   $92.55   $92.50  
  Purchase #3 $227.73   12.550%   $256.3101   $256.31   $256.30   $256.30  
  Purchase #4 $83.46   6.314%   $88.7297   $88.73   $88.75   $88.70  
  Purchase #5 $149.29   8.709%   $162.2917   $162.29   $162.30   $162.30  
  Purchase #6 $192.56   9.178%   $210.2332   $210.23   $210.25   $210.20  
  Purchase #7 $106.64   8.839%   $116.0659   $116.07   $116.05   $116.10  
  7 purchase totals = $908.09       $994.7134   $994.71   $994.75   $994.60