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 $199.41   4.823%   $209.0275   $209.03   $209.05   $209.00  
  Purchase #2 $242.56   12.402%   $272.6423   $272.64   $272.65   $272.60  
  Purchase #3 $33.45   4.577%   $34.981   $34.98   $35.00   $35.00  
  Purchase #4 $48.27   7.605%   $51.9409   $51.94   $51.95   $51.90  
  Purchase #5 $220.30   8.394%   $238.792   $238.79   $238.80   $238.80  
  Purchase #6 $67.86   13.767%   $77.2023   $77.20   $77.20   $77.20  
  Purchase #7 $129.63   5.395%   $136.6235   $136.62   $136.60   $136.60  
  7 purchase totals = $941.48       $1,021.2095   $1,021.20   $1,021.25   $1,021.10