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 $99.67   3.499%   $103.1575   $103.16   $103.15   $103.20  
  Purchase #2 $173.36   6.556%   $184.7255   $184.73   $184.75   $184.70  
  Purchase #3 $159.68   8.747%   $173.6472   $173.65   $173.65   $173.60  
  Purchase #4 $225.78   8.199%   $244.2917   $244.29   $244.30   $244.30  
  Purchase #5 $178.60   10.393%   $197.1619   $197.16   $197.15   $197.20  
  Purchase #6 $37.83   9.708%   $41.5025   $41.50   $41.50   $41.50  
  Purchase #7 $84.71   5.299%   $89.1988   $89.20   $89.20   $89.20  
  7 purchase totals = $959.63       $1,033.6851   $1,033.69   $1,033.70   $1,033.70