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	$49.90	10.474%	$55.1265	$55.13	$55.15	$55.10
Purchase #2	$146.49	10.619%	$162.0458	$162.05	$162.05	$162.00
Purchase #3	$250.42	13.120%	$283.2751	$283.28	$283.30	$283.30
Purchase #4	$129.58	10.669%	$143.4049	$143.40	$143.40	$143.40
Purchase #5	$173.31	10.265%	$191.1003	$191.10	$191.10	$191.10
Purchase #6	$89.78	5.300%	$94.5383	$94.54	$94.55	$94.50
Purchase #7	$214.33	10.820%	$237.5205	$237.52	$237.50	$237.50
7 purchase totals =	$1,053.81		$1,167.0114	$1,167.02	$1,167.05	$1,166.90