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 $178.97   6.547%   $190.6872   $190.69   $190.70   $190.70  
  Purchase #2 $68.87   9.430%   $75.3644   $75.36   $75.35   $75.40  
  Purchase #3 $112.97   11.443%   $125.8972   $125.90   $125.90   $125.90  
  Purchase #4 $154.59   12.357%   $173.6927   $173.69   $173.70   $173.70  
  Purchase #5 $104.37   8.809%   $113.564   $113.56   $113.55   $113.60  
  Purchase #6 $224.78   9.739%   $246.6713   $246.67   $246.65   $246.70  
  Purchase #7 $151.69   6.652%   $161.7804   $161.78   $161.80   $161.80  
  7 purchase totals = $996.24       $1,087.6572   $1,087.65   $1,087.65   $1,087.80