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	$250.43	5.621%	$264.5067	$264.51	$264.50	$264.50
Purchase #2	$206.56	3.783%	$214.3742	$214.37	$214.35	$214.40
Purchase #3	$138.35	10.558%	$152.957	$152.96	$152.95	$153.00
Purchase #4	$82.57	9.523%	$90.4331	$90.43	$90.45	$90.40
Purchase #5	$246.94	10.662%	$273.2687	$273.27	$273.25	$273.30
Purchase #6	$239.25	6.483%	$254.7606	$254.76	$254.75	$254.80
Purchase #7	$235.33	5.742%	$248.8426	$248.84	$248.85	$248.80
7 purchase totals =	$1,399.43		$1,499.1429	$1,499.14	$1,499.10	$1,499.20