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 $56.31   6.618%   $60.0366   $60.04   $60.05   $60.00  
  Purchase #2 $228.42   6.315%   $242.8447   $242.84   $242.85   $242.80  
  Purchase #3 $14.56   11.295%   $16.2046   $16.20   $16.20   $16.20  
  Purchase #4 $62.69   12.660%   $70.6266   $70.63   $70.65   $70.60  
  Purchase #5 $182.33   7.669%   $196.3129   $196.31   $196.30   $196.30  
  Purchase #6 $169.94   13.239%   $192.4384   $192.44   $192.45   $192.40  
  Purchase #7 $218.75   8.224%   $236.74   $236.74   $236.75   $236.70  
  7 purchase totals = $933.00       $1,015.2038   $1,015.20   $1,015.25   $1,015.00