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 $138.89   5.661%   $146.7526   $146.75   $146.75   $146.80  
  Purchase #2 $164.32   8.126%   $177.6726   $177.67   $177.65   $177.70  
  Purchase #3 $129.37   9.477%   $141.6304   $141.63   $141.65   $141.60  
  Purchase #4 $205.53   13.410%   $233.0916   $233.09   $233.10   $233.10  
  Purchase #5 $50.90   8.414%   $55.1827   $55.18   $55.20   $55.20  
  Purchase #6 $168.95   12.385%   $189.8745   $189.87   $189.85   $189.90  
  Purchase #7 $153.84   5.568%   $162.4058   $162.41   $162.40   $162.40  
  7 purchase totals = $1,011.80       $1,106.6102   $1,106.60   $1,106.60   $1,106.70