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	$244.72	9.294%	$267.4643	$267.46	$267.45	$267.50
Purchase #2	$195.69	4.231%	$203.9696	$203.97	$203.95	$204.00
Purchase #3	$231.31	6.834%	$247.1177	$247.12	$247.10	$247.10
Purchase #4	$127.64	10.142%	$140.5852	$140.59	$140.60	$140.60
Purchase #5	$168.77	13.335%	$191.2755	$191.28	$191.30	$191.30
Purchase #6	$36.31	3.570%	$37.6063	$37.61	$37.60	$37.60
Purchase #7	$168.31	6.309%	$178.9287	$178.93	$178.95	$178.90
7 purchase totals =	$1,172.75		$1,266.9473	$1,266.96	$1,266.95	$1,267.00