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 $50.58   7.396%   $54.3209   $54.32   $54.30   $54.30  
  Purchase #2 $26.60   8.548%   $28.8738   $28.87   $28.85   $28.90  
  Purchase #3 $147.53   13.172%   $166.9627   $166.96   $166.95   $167.00  
  Purchase #4 $232.94   4.584%   $243.618   $243.62   $243.60   $243.60  
  Purchase #5 $35.30   3.495%   $36.5337   $36.53   $36.55   $36.50  
  Purchase #6 $117.38   7.337%   $125.9922   $125.99   $126.00   $126.00  
  Purchase #7 $91.45   4.717%   $95.7637   $95.76   $95.75   $95.80  
  7 purchase totals = $701.78       $752.0650   $752.05   $752.00   $752.10