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 $192.40   11.698%   $214.907   $214.91   $214.90   $214.90  
  Purchase #2 $125.27   4.274%   $130.624   $130.62   $130.60   $130.60  
  Purchase #3 $211.82   6.242%   $225.0418   $225.04   $225.05   $225.00  
  Purchase #4 $174.50   6.331%   $185.5476   $185.55   $185.55   $185.50  
  Purchase #5 $220.45   10.675%   $243.983   $243.98   $244.00   $244.00  
  Purchase #6 $236.27   9.330%   $258.314   $258.31   $258.30   $258.30  
  Purchase #7 $50.78   8.829%   $55.2634   $55.26   $55.25   $55.30  
  7 purchase totals = $1,211.49       $1,313.6808   $1,313.67   $1,313.65   $1,313.60