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 $51.93   5.782%   $54.9326   $54.93   $54.95   $54.90  
  Purchase #2 $213.58   9.412%   $233.6821   $233.68   $233.70   $233.70  
  Purchase #3 $175.58   13.379%   $199.0708   $199.07   $199.05   $199.10  
  Purchase #4 $97.48   7.498%   $104.7891   $104.79   $104.80   $104.80  
  Purchase #5 $237.88   3.221%   $245.5421   $245.54   $245.55   $245.50  
  Purchase #6 $95.45   13.704%   $108.5305   $108.53   $108.55   $108.50  
  Purchase #7 $64.61   6.274%   $68.6636   $68.66   $68.65   $68.70  
  7 purchase totals = $936.51       $1,015.2108   $1,015.20   $1,015.25   $1,015.20