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 $204.70   7.605%   $220.2674   $220.27   $220.25   $220.30  
  Purchase #2 $213.29   5.710%   $225.4689   $225.47   $225.45   $225.50  
  Purchase #3 $46.84   12.872%   $52.8692   $52.87   $52.85   $52.90  
  Purchase #4 $71.64   6.500%   $76.2966   $76.30   $76.30   $76.30  
  Purchase #5 $53.83   9.251%   $58.8098   $58.81   $58.80   $58.80  
  Purchase #6 $241.57   11.281%   $268.8215   $268.82   $268.80   $268.80  
  Purchase #7 $125.74   8.448%   $136.3625   $136.36   $136.35   $136.40  
  7 purchase totals = $957.61       $1,038.8959   $1,038.90   $1,038.80   $1,039.00