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 $69.89   8.252%   $75.6573   $75.66   $75.65   $75.70  
  Purchase #2 $209.84   7.845%   $226.3019   $226.30   $226.30   $226.30  
  Purchase #3 $113.46   10.314%   $125.1623   $125.16   $125.15   $125.20  
  Purchase #4 $137.80   4.752%   $144.3483   $144.35   $144.35   $144.30  
  Purchase #5 $165.83   5.659%   $175.2143   $175.21   $175.20   $175.20  
  Purchase #6 $64.30   13.468%   $72.9599   $72.96   $72.95   $73.00  
  Purchase #7 $72.73   9.383%   $79.5543   $79.55   $79.55   $79.60  
  7 purchase totals = $833.85       $899.1983   $899.19   $899.15   $899.30