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 $182.75   6.852%   $195.272   $195.27   $195.25   $195.30  
  Purchase #2 $242.54   3.477%   $250.9731   $250.97   $250.95   $251.00  
  Purchase #3 $87.81   12.726%   $98.9847   $98.98   $99.00   $99.00  
  Purchase #4 $183.97   11.250%   $204.6666   $204.67   $204.65   $204.70  
  Purchase #5 $152.74   11.720%   $170.6411   $170.64   $170.65   $170.60  
  Purchase #6 $56.75   10.248%   $62.5657   $62.57   $62.55   $62.60  
  Purchase #7 $49.35   7.729%   $53.1643   $53.16   $53.15   $53.20  
  7 purchase totals = $955.91       $1,036.2675   $1,036.26   $1,036.20   $1,036.40