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 $208.93   7.105%   $223.7745   $223.77   $223.75   $223.80  
  Purchase #2 $73.41   10.604%   $81.1944   $81.19   $81.20   $81.20  
  Purchase #3 $135.71   9.484%   $148.5807   $148.58   $148.60   $148.60  
  Purchase #4 $118.98   6.159%   $126.308   $126.31   $126.30   $126.30  
  Purchase #5 $161.59   5.782%   $170.9331   $170.93   $170.95   $170.90  
  Purchase #6 $236.68   10.142%   $260.6841   $260.68   $260.70   $260.70  
  Purchase #7 $51.62   13.308%   $58.4896   $58.49   $58.50   $58.50  
  7 purchase totals = $986.92       $1,069.9644   $1,069.95   $1,070.00   $1,070.00