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 $238.95   12.687%   $269.2656   $269.27   $269.25   $269.30  
  Purchase #2 $213.72   5.279%   $225.0023   $225.00   $225.00   $225.00  
  Purchase #3 $76.75   4.615%   $80.292   $80.29   $80.30   $80.30  
  Purchase #4 $215.94   11.152%   $240.0216   $240.02   $240.00   $240.00  
  Purchase #5 $234.63   10.403%   $259.0386   $259.04   $259.05   $259.00  
  Purchase #6 $215.67   13.552%   $244.8976   $244.90   $244.90   $244.90  
  Purchase #7 $128.87   11.343%   $143.4877   $143.49   $143.50   $143.50  
  7 purchase totals = $1,324.53       $1,462.0054   $1,462.01   $1,462.00   $1,462.00