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 $219.63   7.591%   $236.3021   $236.30   $236.30   $236.30  
  Purchase #2 $127.28   10.709%   $140.9104   $140.91   $140.90   $140.90  
  Purchase #3 $65.86   11.583%   $73.4886   $73.49   $73.50   $73.50  
  Purchase #4 $60.90   4.791%   $63.8177   $63.82   $63.80   $63.80  
  Purchase #5 $44.53   5.588%   $47.0183   $47.02   $47.00   $47.00  
  Purchase #6 $101.97   6.368%   $108.4634   $108.46   $108.45   $108.50  
  Purchase #7 $91.58   8.404%   $99.2764   $99.28   $99.30   $99.30  
  7 purchase totals = $711.75       $769.2769   $769.28   $769.25   $769.30