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 $183.62   13.773%   $208.91   $208.91   $208.90   $208.90  
  Purchase #2 $87.91   7.111%   $94.1613   $94.16   $94.15   $94.20  
  Purchase #3 $221.28   11.617%   $246.9861   $246.99   $247.00   $247.00  
  Purchase #4 $178.28   9.520%   $195.2523   $195.25   $195.25   $195.30  
  Purchase #5 $146.91   9.203%   $160.4301   $160.43   $160.45   $160.40  
  Purchase #6 $108.41   3.412%   $112.1089   $112.11   $112.10   $112.10  
  Purchase #7 $26.43   8.530%   $28.6845   $28.68   $28.70   $28.70  
  7 purchase totals = $952.84       $1,046.5332   $1,046.53   $1,046.55   $1,046.60