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	$64.57	12.302%	$72.5134	$72.51	$72.50	$72.50
Purchase #2	$230.56	8.250%	$249.5812	$249.58	$249.60	$249.60
Purchase #3	$231.28	5.546%	$244.1068	$244.11	$244.10	$244.10
Purchase #4	$145.30	6.297%	$154.4495	$154.45	$154.45	$154.40
Purchase #5	$153.32	7.290%	$164.497	$164.50	$164.50	$164.50
Purchase #6	$197.78	5.427%	$208.5135	$208.51	$208.50	$208.50
Purchase #7	$75.91	12.713%	$85.5604	$85.56	$85.55	$85.60
7 purchase totals =	$1,098.72		$1,179.2218	$1,179.22	$1,179.20	$1,179.20