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 $183.32   12.672%   $206.5503   $206.55   $206.55   $206.60  
  Purchase #2 $185.40   5.179%   $195.0019   $195.00   $195.00   $195.00  
  Purchase #3 $57.35   12.459%   $64.4952   $64.50   $64.50   $64.50  
  Purchase #4 $164.77   3.482%   $170.5073   $170.51   $170.50   $170.50  
  Purchase #5 $43.79   4.222%   $45.6388   $45.64   $45.65   $45.60  
  Purchase #6 $146.26   9.176%   $159.6808   $159.68   $159.70   $159.70  
  Purchase #7 $99.91   3.231%   $103.1381   $103.14   $103.15   $103.10  
  7 purchase totals = $880.80       $945.0124   $945.02   $945.05   $945.00