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 $231.63   13.235%   $262.2862   $262.29   $262.30   $262.30  
  Purchase #2 $168.39   6.681%   $179.6401   $179.64   $179.65   $179.60  
  Purchase #3 $178.64   9.302%   $195.2571   $195.26   $195.25   $195.30  
  Purchase #4 $84.33   9.347%   $92.2123   $92.21   $92.20   $92.20  
  Purchase #5 $91.78   8.573%   $99.6483   $99.65   $99.65   $99.60  
  Purchase #6 $71.61   12.223%   $80.3629   $80.36   $80.35   $80.40  
  Purchase #7 $127.65   13.207%   $144.5087   $144.51   $144.50   $144.50  
  7 purchase totals = $954.03       $1,053.9156   $1,053.92   $1,053.90   $1,053.90