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 $66.85   11.453%   $74.5063   $74.51   $74.50   $74.50  
  Purchase #2 $141.41   8.316%   $153.1697   $153.17   $153.15   $153.20  
  Purchase #3 $90.73   8.664%   $98.5908   $98.59   $98.60   $98.60  
  Purchase #4 $238.52   3.574%   $247.0447   $247.04   $247.05   $247.00  
  Purchase #5 $211.49   12.807%   $238.5755   $238.58   $238.60   $238.60  
  Purchase #6 $5.85   4.682%   $6.1239   $6.12   $6.10   $6.10  
  Purchase #7 $61.86   4.117%   $64.4068   $64.41   $64.40   $64.40  
  7 purchase totals = $816.71       $882.4177   $882.42   $882.40   $882.40