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 $119.98   4.319%   $125.1619   $125.16   $125.15   $125.20  
  Purchase #2 $225.55   10.557%   $249.3613   $249.36   $249.35   $249.40  
  Purchase #3 $147.60   12.648%   $166.2684   $166.27   $166.25   $166.30  
  Purchase #4 $36.26   12.434%   $40.7686   $40.77   $40.75   $40.80  
  Purchase #5 $106.42   11.371%   $118.521   $118.52   $118.50   $118.50  
  Purchase #6 $58.54   6.831%   $62.5389   $62.54   $62.55   $62.50  
  Purchase #7 $9.71   11.395%   $10.8165   $10.82   $10.80   $10.80  
  7 purchase totals = $704.06       $773.4366   $773.44   $773.35   $773.50