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 $215.26   7.290%   $230.9525   $230.95   $230.95   $231.00  
  Purchase #2 $64.54   5.226%   $67.9129   $67.91   $67.90   $67.90  
  Purchase #3 $208.62   3.766%   $216.4766   $216.48   $216.50   $216.50  
  Purchase #4 $52.74   5.850%   $55.8253   $55.83   $55.85   $55.80  
  Purchase #5 $125.87   7.631%   $135.4751   $135.48   $135.50   $135.50  
  Purchase #6 $89.42   10.232%   $98.5695   $98.57   $98.55   $98.60  
  Purchase #7 $53.28   8.731%   $57.9319   $57.93   $57.95   $57.90  
  7 purchase totals = $809.73       $863.1438   $863.15   $863.20   $863.20