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 $235.98   10.166%   $259.9697   $259.97   $259.95   $260.00  
  Purchase #2 $117.56   5.366%   $123.8683   $123.87   $123.85   $123.90  
  Purchase #3 $5.84   10.387%   $6.4466   $6.45   $6.45   $6.40  
  Purchase #4 $205.72   13.867%   $234.2472   $234.25   $234.25   $234.20  
  Purchase #5 $114.88   4.277%   $119.7934   $119.79   $119.80   $119.80  
  Purchase #6 $109.61   8.325%   $118.735   $118.74   $118.75   $118.70  
  Purchase #7 $94.26   7.172%   $101.0203   $101.02   $101.00   $101.00  
  7 purchase totals = $883.85       $964.0805   $964.09   $964.05   $964.00