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 $45.82   13.493%   $52.0025   $52.00   $52.00   $52.00  
  Purchase #2 $201.55   7.530%   $216.7267   $216.73   $216.75   $216.70  
  Purchase #3 $16.63   3.520%   $17.2154   $17.22   $17.20   $17.20  
  Purchase #4 $170.59   3.163%   $175.9858   $175.99   $176.00   $176.00  
  Purchase #5 $217.96   12.868%   $246.0071   $246.01   $246.00   $246.00  
  Purchase #6 $91.97   11.591%   $102.6302   $102.63   $102.65   $102.60  
  Purchase #7 $139.74   10.477%   $154.3806   $154.38   $154.40   $154.40  
  7 purchase totals = $884.26       $964.9483   $964.96   $965.00   $964.90