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	$129.83	10.832%	$143.8932	$143.89	$143.90	$143.90
Purchase #2	$212.52	7.475%	$228.4059	$228.41	$228.40	$228.40
Purchase #3	$235.35	12.230%	$264.1333	$264.13	$264.15	$264.10
Purchase #4	$89.54	10.764%	$99.1781	$99.18	$99.20	$99.20
Purchase #5	$94.58	12.655%	$106.5491	$106.55	$106.55	$106.50
Purchase #6	$211.90	10.404%	$233.9461	$233.95	$233.95	$233.90
Purchase #7	$151.85	3.498%	$157.1617	$157.16	$157.15	$157.20
7 purchase totals =	$1,125.57		$1,233.2674	$1,233.27	$1,233.30	$1,233.20