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	$144.33	6.473%	$153.6725	$153.67	$153.65	$153.70
Purchase #2	$143.83	6.250%	$152.8194	$152.82	$152.80	$152.80
Purchase #3	$67.50	9.426%	$73.8626	$73.86	$73.85	$73.90
Purchase #4	$173.29	7.310%	$185.9575	$185.96	$185.95	$186.00
Purchase #5	$95.68	4.287%	$99.7818	$99.78	$99.80	$99.80
Purchase #6	$151.98	13.476%	$172.4608	$172.46	$172.45	$172.50
Purchase #7	$37.76	4.715%	$39.5404	$39.54	$39.55	$39.50
7 purchase totals =	$814.37		$878.0950	$878.09	$878.05	$878.20