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 $65.41   12.691%   $73.7112   $73.71   $73.70   $73.70  
  Purchase #2 $241.73   12.305%   $271.4749   $271.47   $271.45   $271.50  
  Purchase #3 $124.27   9.812%   $136.4634   $136.46   $136.45   $136.50  
  Purchase #4 $40.59   5.583%   $42.8561   $42.86   $42.85   $42.90  
  Purchase #5 $174.73   7.478%   $187.7963   $187.80   $187.80   $187.80  
  Purchase #6 $187.75   7.350%   $201.5496   $201.55   $201.55   $201.50  
  Purchase #7 $36.27   10.841%   $40.202   $40.20   $40.20   $40.20  
  7 purchase totals = $870.75       $954.0535   $954.05   $954.00   $954.10