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 $198.34   4.848%   $207.9555   $207.96   $207.95   $208.00  
  Purchase #2 $242.35   10.799%   $268.5214   $268.52   $268.50   $268.50  
  Purchase #3 $117.40   13.455%   $133.1962   $133.20   $133.20   $133.20  
  Purchase #4 $173.33   12.779%   $195.4798   $195.48   $195.50   $195.50  
  Purchase #5 $72.80   5.716%   $76.9612   $76.96   $76.95   $77.00  
  Purchase #6 $213.78   12.507%   $240.5175   $240.52   $240.50   $240.50  
  Purchase #7 $32.95   3.580%   $34.1296   $34.13   $34.15   $34.10  
  7 purchase totals = $1,050.95       $1,156.7612   $1,156.77   $1,156.75   $1,156.80