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	$147.42	6.236%	$156.6131	$156.61	$156.60	$156.60
Purchase #2	$61.63	6.741%	$65.7845	$65.78	$65.80	$65.80
Purchase #3	$125.90	3.146%	$129.8608	$129.86	$129.85	$129.90
Purchase #4	$75.45	9.428%	$82.5634	$82.56	$82.55	$82.60
Purchase #5	$190.80	5.254%	$200.8246	$200.82	$200.80	$200.80
Purchase #6	$199.28	10.123%	$219.4531	$219.45	$219.45	$219.50
Purchase #7	$220.99	13.436%	$250.6822	$250.68	$250.70	$250.70
7 purchase totals =	$1,021.47		$1,105.7817	$1,105.76	$1,105.75	$1,105.90