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 $113.95   10.224%   $125.6002   $125.60   $125.60   $125.60  
  Purchase #2 $70.97   9.796%   $77.9222   $77.92   $77.90   $77.90  
  Purchase #3 $101.33   6.493%   $107.9094   $107.91   $107.90   $107.90  
  Purchase #4 $248.26   12.201%   $278.5502   $278.55   $278.55   $278.60  
  Purchase #5 $182.32   4.703%   $190.8945   $190.89   $190.90   $190.90  
  Purchase #6 $103.94   8.843%   $113.1314   $113.13   $113.15   $113.10  
  Purchase #7 $93.91   13.845%   $106.9118   $106.91   $106.90   $106.90  
  7 purchase totals = $914.68       $1,000.9197   $1,000.91   $1,000.90   $1,000.90