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 $68.25   8.299%   $73.9141   $73.91   $73.90   $73.90  
  Purchase #2 $154.54   13.454%   $175.3318   $175.33   $175.35   $175.30  
  Purchase #3 $151.34   9.246%   $165.3329   $165.33   $165.35   $165.30  
  Purchase #4 $143.93   11.275%   $160.1581   $160.16   $160.15   $160.20  
  Purchase #5 $119.85   10.461%   $132.3875   $132.39   $132.40   $132.40  
  Purchase #6 $57.55   10.662%   $63.686   $63.69   $63.70   $63.70  
  Purchase #7 $44.31   8.379%   $48.0227   $48.02   $48.00   $48.00  
  7 purchase totals = $739.77       $818.8331   $818.83   $818.85   $818.80