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 $7.85   5.146%   $8.254   $8.25   $8.25   $8.30  
  Purchase #2 $231.51   13.381%   $262.4884   $262.49   $262.50   $262.50  
  Purchase #3 $8.61   4.485%   $8.9962   $9.00   $9.00   $9.00  
  Purchase #4 $132.51   5.607%   $139.9398   $139.94   $139.95   $139.90  
  Purchase #5 $78.29   8.777%   $85.1615   $85.16   $85.15   $85.20  
  Purchase #6 $111.73   5.432%   $117.7992   $117.80   $117.80   $117.80  
  Purchase #7 $105.25   11.578%   $117.4358   $117.44   $117.45   $117.40  
  7 purchase totals = $675.75       $740.0749   $740.08   $740.10   $740.10