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	$68.50	6.727%	$73.108	$73.11	$73.10	$73.10
Purchase #2	$243.92	7.624%	$262.5165	$262.52	$262.50	$262.50
Purchase #3	$55.77	11.722%	$62.3074	$62.31	$62.30	$62.30
Purchase #4	$223.28	4.703%	$233.7809	$233.78	$233.80	$233.80
Purchase #5	$233.39	10.510%	$257.9193	$257.92	$257.90	$257.90
Purchase #6	$196.89	3.497%	$203.7752	$203.78	$203.80	$203.80
Purchase #7	$118.72	13.329%	$134.5442	$134.54	$134.55	$134.50
7 purchase totals =	$1,140.47		$1,227.9515	$1,227.96	$1,227.95	$1,227.90