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 $178.67   6.845%   $190.9   $190.90   $190.90   $190.90  
  Purchase #2 $204.61   6.484%   $217.8769   $217.88   $217.90   $217.90  
  Purchase #3 $111.89   6.677%   $119.3609   $119.36   $119.35   $119.40  
  Purchase #4 $64.54   5.241%   $67.9225   $67.92   $67.90   $67.90  
  Purchase #5 $104.53   9.723%   $114.6935   $114.69   $114.70   $114.70  
  Purchase #6 $154.82   10.255%   $170.6968   $170.70   $170.70   $170.70  
  Purchase #7 $12.56   6.207%   $13.3396   $13.34   $13.35   $13.30  
  7 purchase totals = $831.62       $894.7902   $894.79   $894.80   $894.80