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 $248.77   7.679%   $267.873   $267.87   $267.85   $267.90  
  Purchase #2 $60.98   9.844%   $66.9829   $66.98   $67.00   $67.00  
  Purchase #3 $71.77   7.829%   $77.3889   $77.39   $77.40   $77.40  
  Purchase #4 $91.85   13.291%   $104.0578   $104.06   $104.05   $104.10  
  Purchase #5 $17.60   11.748%   $19.6676   $19.67   $19.65   $19.70  
  Purchase #6 $146.32   10.733%   $162.0245   $162.02   $162.00   $162.00  
  Purchase #7 $64.90   13.222%   $73.4811   $73.48   $73.50   $73.50  
  7 purchase totals = $702.19       $771.4758   $771.47   $771.45   $771.60