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	$25.47	12.453%	$28.6418	$28.64	$28.65	$28.60
Purchase #2	$218.35	4.827%	$228.8898	$228.89	$228.90	$228.90
Purchase #3	$194.60	11.263%	$216.5178	$216.52	$216.50	$216.50
Purchase #4	$64.90	8.480%	$70.4035	$70.40	$70.40	$70.40
Purchase #5	$21.86	9.406%	$23.9162	$23.92	$23.90	$23.90
Purchase #6	$168.92	13.140%	$191.1161	$191.12	$191.10	$191.10
Purchase #7	$119.52	6.391%	$127.1585	$127.16	$127.15	$127.20
7 purchase totals =	$813.62		$886.6437	$886.65	$886.60	$886.60