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 $209.92   13.242%   $237.7176   $237.72   $237.70   $237.70  
  Purchase #2 $178.43   10.719%   $197.5559   $197.56   $197.55   $197.60  
  Purchase #3 $225.92   3.417%   $233.6397   $233.64   $233.65   $233.60  
  Purchase #4 $172.89   13.124%   $195.5801   $195.58   $195.60   $195.60  
  Purchase #5 $124.47   8.614%   $135.1918   $135.19   $135.20   $135.20  
  Purchase #6 $11.29   12.116%   $12.6579   $12.66   $12.65   $12.70  
  Purchase #7 $174.83   9.785%   $191.9371   $191.94   $191.95   $191.90  
  7 purchase totals = $1,097.75       $1,204.2801   $1,204.29   $1,204.30   $1,204.30