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	$45.44	9.430%	$49.725	$49.73	$49.75	$49.70
Purchase #2	$90.59	12.450%	$101.8685	$101.87	$101.85	$101.90
Purchase #3	$6.66	13.356%	$7.5495	$7.55	$7.55	$7.50
Purchase #4	$211.71	7.481%	$227.548	$227.55	$227.55	$227.50
Purchase #5	$215.45	11.777%	$240.8235	$240.82	$240.80	$240.80
Purchase #6	$143.93	8.778%	$156.5642	$156.56	$156.55	$156.60
Purchase #7	$203.34	9.562%	$222.7834	$222.78	$222.80	$222.80
7 purchase totals =	$917.12		$1,006.8621	$1,006.86	$1,006.85	$1,006.80