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 $136.78   6.683%   $145.921   $145.92   $145.90   $145.90  
  Purchase #2 $84.87   11.136%   $94.3211   $94.32   $94.30   $94.30  
  Purchase #3 $240.93   8.739%   $261.9849   $261.98   $262.00   $262.00  
  Purchase #4 $169.81   7.705%   $182.8939   $182.89   $182.90   $182.90  
  Purchase #5 $234.39   9.426%   $256.4836   $256.48   $256.50   $256.50  
  Purchase #6 $230.94   13.820%   $262.8559   $262.86   $262.85   $262.90  
  Purchase #7 $244.82   4.641%   $256.1821   $256.18   $256.20   $256.20  
  7 purchase totals = $1,342.54       $1,460.6425   $1,460.63   $1,460.65   $1,460.70