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	$244.25	4.717%	$255.7713	$255.77	$255.75	$255.80
Purchase #2	$36.34	10.342%	$40.0983	$40.10	$40.10	$40.10
Purchase #3	$117.39	6.455%	$124.9675	$124.97	$124.95	$125.00
Purchase #4	$137.74	4.227%	$143.5623	$143.56	$143.55	$143.60
Purchase #5	$78.92	13.142%	$89.2917	$89.29	$89.30	$89.30
Purchase #6	$7.75	3.798%	$8.0443	$8.04	$8.05	$8.00
Purchase #7	$249.75	12.553%	$281.1011	$281.10	$281.10	$281.10
7 purchase totals =	$872.14		$942.8365	$942.83	$942.80	$942.90