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 $209.35   11.762%   $233.9737   $233.97   $233.95   $234.00  
  Purchase #2 $35.30   9.775%   $38.7506   $38.75   $38.75   $38.80  
  Purchase #3 $14.27   9.570%   $15.6356   $15.64   $15.65   $15.60  
  Purchase #4 $139.63   7.136%   $149.594   $149.59   $149.60   $149.60  
  Purchase #5 $223.87   11.687%   $250.0337   $250.03   $250.05   $250.00  
  Purchase #6 $185.76   9.745%   $203.8623   $203.86   $203.85   $203.90  
  Purchase #7 $58.28   4.854%   $61.1089   $61.11   $61.10   $61.10  
  7 purchase totals = $866.46       $952.9588   $952.95   $952.95   $953.00