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 $111.79   11.830%   $125.0148   $125.01   $125.00   $125.00  
  Purchase #2 $40.75   4.227%   $42.4725   $42.47   $42.45   $42.50  
  Purchase #3 $201.30   6.309%   $214   $214.00   $214.00   $214.00  
  Purchase #4 $186.34   4.699%   $195.0961   $195.10   $195.10   $195.10  
  Purchase #5 $223.84   4.621%   $234.1836   $234.18   $234.20   $234.20  
  Purchase #6 $109.96   13.654%   $124.9739   $124.97   $124.95   $125.00  
  Purchase #7 $250.99   4.787%   $263.0049   $263.00   $263.00   $263.00  
  7 purchase totals = $1,124.97       $1,198.7458   $1,198.73   $1,198.70   $1,198.80