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 $220.63   10.683%   $244.1999   $244.20   $244.20   $244.20  
  Purchase #2 $117.69   3.267%   $121.5349   $121.53   $121.55   $121.50  
  Purchase #3 $103.80   4.307%   $108.2707   $108.27   $108.25   $108.30  
  Purchase #4 $26.94   4.402%   $28.1259   $28.13   $28.15   $28.10  
  Purchase #5 $70.73   3.570%   $73.2551   $73.26   $73.25   $73.30  
  Purchase #6 $182.97   8.534%   $198.5847   $198.58   $198.60   $198.60  
  Purchase #7 $38.26   12.340%   $42.9813   $42.98   $43.00   $43.00  
  7 purchase totals = $761.02       $816.9525   $816.95   $817.00   $817.00