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 $244.90   11.560%   $273.2104   $273.21   $273.20   $273.20  
  Purchase #2 $55.93   10.150%   $61.6069   $61.61   $61.60   $61.60  
  Purchase #3 $181.63   6.409%   $193.2707   $193.27   $193.25   $193.30  
  Purchase #4 $107.33   13.452%   $121.768   $121.77   $121.75   $121.80  
  Purchase #5 $141.94   7.871%   $153.1121   $153.11   $153.10   $153.10  
  Purchase #6 $217.43   7.776%   $234.3374   $234.34   $234.35   $234.30  
  Purchase #7 $170.29   11.267%   $189.4766   $189.48   $189.50   $189.50  
  7 purchase totals = $1,119.45       $1,226.7821   $1,226.79   $1,226.75   $1,226.80