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	$82.76	9.221%	$90.3913	$90.39	$90.40	$90.40
Purchase #2	$241.66	5.591%	$255.1712	$255.17	$255.15	$255.20
Purchase #3	$79.50	3.573%	$82.3405	$82.34	$82.35	$82.30
Purchase #4	$200.48	5.129%	$210.7626	$210.76	$210.75	$210.80
Purchase #5	$9.45	12.267%	$10.6092	$10.61	$10.60	$10.60
Purchase #6	$165.48	9.455%	$181.1261	$181.13	$181.15	$181.10
Purchase #7	$94.27	5.690%	$99.634	$99.63	$99.65	$99.60
7 purchase totals =	$873.60		$930.0349	$930.03	$930.05	$930.00