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 $127.49   5.367%   $134.3324   $134.33   $134.35   $134.30  
  Purchase #2 $82.67   3.291%   $85.3907   $85.39   $85.40   $85.40  
  Purchase #3 $72.72   5.720%   $76.8796   $76.88   $76.90   $76.90  
  Purchase #4 $91.92   4.167%   $95.7503   $95.75   $95.75   $95.80  
  Purchase #5 $163.41   11.479%   $182.1678   $182.17   $182.15   $182.20  
  Purchase #6 $103.67   12.681%   $116.8164   $116.82   $116.80   $116.80  
  Purchase #7 $61.37   11.292%   $68.2999   $68.30   $68.30   $68.30  
  7 purchase totals = $703.25       $759.6371   $759.64   $759.65   $759.70