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 $230.47   3.103%   $237.6215   $237.62   $237.60   $237.60  
  Purchase #2 $192.88   4.871%   $202.2752   $202.28   $202.30   $202.30  
  Purchase #3 $18.67   10.151%   $20.5652   $20.57   $20.55   $20.60  
  Purchase #4 $51.30   11.694%   $57.299   $57.30   $57.30   $57.30  
  Purchase #5 $206.35   11.681%   $230.4537   $230.45   $230.45   $230.50  
  Purchase #6 $199.39   7.664%   $214.6712   $214.67   $214.65   $214.70  
  Purchase #7 $51.98   12.422%   $58.437   $58.44   $58.45   $58.40  
  7 purchase totals = $951.04       $1,021.3228   $1,021.33   $1,021.30   $1,021.40