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 $68.66   12.497%   $77.2404   $77.24   $77.25   $77.20  
  Purchase #2 $246.98   8.403%   $267.7337   $267.73   $267.75   $267.70  
  Purchase #3 $41.91   8.183%   $45.3395   $45.34   $45.35   $45.30  
  Purchase #4 $26.26   13.713%   $29.861   $29.86   $29.85   $29.90  
  Purchase #5 $240.35   12.817%   $271.1557   $271.16   $271.15   $271.20  
  Purchase #6 $226.65   11.838%   $253.4808   $253.48   $253.50   $253.50  
  Purchase #7 $33.32   9.853%   $36.603   $36.60   $36.60   $36.60  
  7 purchase totals = $884.13       $981.4141   $981.41   $981.45   $981.40