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 $228.81   7.395%   $245.7305   $245.73   $245.75   $245.70  
  Purchase #2 $164.37   7.168%   $176.152   $176.15   $176.15   $176.20  
  Purchase #3 $123.67   11.276%   $137.615   $137.62   $137.60   $137.60  
  Purchase #4 $225.34   5.602%   $237.9635   $237.96   $237.95   $238.00  
  Purchase #5 $159.37   10.146%   $175.5397   $175.54   $175.55   $175.50  
  Purchase #6 $87.53   9.347%   $95.7114   $95.71   $95.70   $95.70  
  Purchase #7 $78.89   12.604%   $88.8333   $88.83   $88.85   $88.80  
  7 purchase totals = $1,067.98       $1,157.5454   $1,157.54   $1,157.55   $1,157.50