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 $224.54   4.551%   $234.7588   $234.76   $234.75   $234.80  
  Purchase #2 $244.82   8.519%   $265.6762   $265.68   $265.70   $265.70  
  Purchase #3 $103.92   13.573%   $118.0251   $118.03   $118.05   $118.00  
  Purchase #4 $164.96   3.435%   $170.6264   $170.63   $170.65   $170.60  
  Purchase #5 $242.28   12.429%   $272.393   $272.39   $272.40   $272.40  
  Purchase #6 $61.50   4.348%   $64.174   $64.17   $64.15   $64.20  
  Purchase #7 $207.49   8.444%   $225.0105   $225.01   $225.00   $225.00  
  7 purchase totals = $1,249.51       $1,350.6640   $1,350.67   $1,350.70   $1,350.70