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 $238.76   5.811%   $252.6343   $252.63   $252.65   $252.60  
  Purchase #2 $174.75   11.256%   $194.4199   $194.42   $194.40   $194.40  
  Purchase #3 $53.34   9.590%   $58.4553   $58.46   $58.45   $58.50  
  Purchase #4 $142.35   3.358%   $147.1301   $147.13   $147.15   $147.10  
  Purchase #5 $165.90   3.303%   $171.3797   $171.38   $171.40   $171.40  
  Purchase #6 $250.91   7.537%   $269.8211   $269.82   $269.80   $269.80  
  Purchase #7 $191.66   9.472%   $209.814   $209.81   $209.80   $209.80  
  7 purchase totals = $1,217.67       $1,303.6544   $1,303.65   $1,303.65   $1,303.60