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 $238.28   11.234%   $265.0484   $265.05   $265.05   $265.00  
  Purchase #2 $175.67   9.656%   $192.6327   $192.63   $192.65   $192.60  
  Purchase #3 $187.90   13.392%   $213.0636   $213.06   $213.05   $213.10  
  Purchase #4 $237.30   10.800%   $262.9284   $262.93   $262.95   $262.90  
  Purchase #5 $217.62   5.257%   $229.0603   $229.06   $229.05   $229.10  
  Purchase #6 $118.68   11.164%   $131.9294   $131.93   $131.95   $131.90  
  Purchase #7 $79.28   7.475%   $85.2062   $85.21   $85.20   $85.20  
  7 purchase totals = $1,254.73       $1,379.8690   $1,379.87   $1,379.90   $1,379.80