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 $195.65   3.732%   $202.9517   $202.95   $202.95   $203.00  
  Purchase #2 $250.36   9.384%   $273.8538   $273.85   $273.85   $273.90  
  Purchase #3 $130.33   7.433%   $140.0174   $140.02   $140.00   $140.00  
  Purchase #4 $129.85   11.394%   $144.6451   $144.65   $144.65   $144.60  
  Purchase #5 $185.30   10.615%   $204.9696   $204.97   $204.95   $205.00  
  Purchase #6 $245.97   10.523%   $271.8534   $271.85   $271.85   $271.90  
  Purchase #7 $21.72   12.680%   $24.4741   $24.47   $24.45   $24.50  
  7 purchase totals = $1,159.18       $1,262.7651   $1,262.76   $1,262.70   $1,262.90