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 $172.41   10.761%   $190.963   $190.96   $190.95   $191.00  
  Purchase #2 $104.98   12.166%   $117.7519   $117.75   $117.75   $117.80  
  Purchase #3 $222.44   7.799%   $239.7881   $239.79   $239.80   $239.80  
  Purchase #4 $168.95   11.109%   $187.7187   $187.72   $187.70   $187.70  
  Purchase #5 $185.80   10.292%   $204.9225   $204.92   $204.90   $204.90  
  Purchase #6 $32.28   3.131%   $33.2907   $33.29   $33.30   $33.30  
  Purchase #7 $244.94   12.743%   $276.1527   $276.15   $276.15   $276.20  
  7 purchase totals = $1,131.80       $1,250.5876   $1,250.58   $1,250.55   $1,250.70