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 $68.32   13.323%   $77.4223   $77.42   $77.40   $77.40  
  Purchase #2 $198.41   11.500%   $221.2272   $221.23   $221.25   $221.20  
  Purchase #3 $241.64   3.839%   $250.9166   $250.92   $250.90   $250.90  
  Purchase #4 $162.49   9.248%   $177.5171   $177.52   $177.50   $177.50  
  Purchase #5 $248.84   10.759%   $275.6127   $275.61   $275.60   $275.60  
  Purchase #6 $101.38   8.552%   $110.05   $110.05   $110.05   $110.10  
  Purchase #7 $93.66   11.632%   $104.5545   $104.55   $104.55   $104.60  
  7 purchase totals = $1,114.74       $1,217.3004   $1,217.30   $1,217.25   $1,217.30