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 $187.95   5.296%   $197.9038   $197.90   $197.90   $197.90  
  Purchase #2 $183.61   6.455%   $195.462   $195.46   $195.45   $195.50  
  Purchase #3 $54.31   10.665%   $60.1022   $60.10   $60.10   $60.10  
  Purchase #4 $230.84   6.686%   $246.274   $246.27   $246.25   $246.30  
  Purchase #5 $28.59   5.177%   $30.0701   $30.07   $30.05   $30.10  
  Purchase #6 $219.46   7.625%   $236.1938   $236.19   $236.20   $236.20  
  Purchase #7 $34.33   4.844%   $35.9929   $35.99   $36.00   $36.00  
  7 purchase totals = $939.09       $1,001.9988   $1,001.98   $1,001.95   $1,002.10