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 $56.46   9.372%   $61.7514   $61.75   $61.75   $61.80  
  Purchase #2 $163.54   11.762%   $182.7756   $182.78   $182.80   $182.80  
  Purchase #3 $110.50   4.235%   $115.1797   $115.18   $115.20   $115.20  
  Purchase #4 $210.26   8.245%   $227.5959   $227.60   $227.60   $227.60  
  Purchase #5 $196.87   8.870%   $214.3324   $214.33   $214.35   $214.30  
  Purchase #6 $46.53   11.543%   $51.901   $51.90   $51.90   $51.90  
  Purchase #7 $111.47   13.468%   $126.4828   $126.48   $126.50   $126.50  
  7 purchase totals = $895.63       $980.0188   $980.02   $980.10   $980.10