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 $8.87   4.131%   $9.2364   $9.24   $9.25   $9.20  
  Purchase #2 $153.67   5.255%   $161.7454   $161.75   $161.75   $161.70  
  Purchase #3 $16.89   10.759%   $18.7072   $18.71   $18.70   $18.70  
  Purchase #4 $82.91   7.146%   $88.8347   $88.83   $88.85   $88.80  
  Purchase #5 $58.98   9.749%   $64.73   $64.73   $64.75   $64.70  
  Purchase #6 $101.80   11.229%   $113.2311   $113.23   $113.25   $113.20  
  Purchase #7 $9.49   9.244%   $10.3673   $10.37   $10.35   $10.40  
  7 purchase totals = $432.61       $466.8521   $466.86   $466.90   $466.70