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 $223.86   11.244%   $249.0308   $249.03   $249.05   $249.00  
  Purchase #2 $200.83   4.552%   $209.9718   $209.97   $209.95   $210.00  
  Purchase #3 $206.53   8.472%   $224.0272   $224.03   $224.05   $224.00  
  Purchase #4 $61.94   3.704%   $64.2343   $64.23   $64.25   $64.20  
  Purchase #5 $78.50   11.671%   $87.6617   $87.66   $87.65   $87.70  
  Purchase #6 $191.69   3.638%   $198.6637   $198.66   $198.65   $198.70  
  Purchase #7 $146.68   11.665%   $163.7902   $163.79   $163.80   $163.80  
  7 purchase totals = $1,110.03       $1,197.3797   $1,197.37   $1,197.40   $1,197.40