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 $190.49   5.672%   $201.2946   $201.29   $201.30   $201.30  
  Purchase #2 $120.54   13.526%   $136.8442   $136.84   $136.85   $136.80  
  Purchase #3 $111.76   8.852%   $121.653   $121.65   $121.65   $121.70  
  Purchase #4 $54.63   7.429%   $58.6885   $58.69   $58.70   $58.70  
  Purchase #5 $16.62   3.871%   $17.2634   $17.26   $17.25   $17.30  
  Purchase #6 $249.80   7.294%   $268.0204   $268.02   $268.00   $268.00  
  Purchase #7 $132.62   9.554%   $145.2905   $145.29   $145.30   $145.30  
  7 purchase totals = $876.46       $949.0546   $949.04   $949.05   $949.10