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	$229.27	9.168%	$250.2895	$250.29	$250.30	$250.30
Purchase #2	$197.74	13.160%	$223.7626	$223.76	$223.75	$223.80
Purchase #3	$154.52	10.422%	$170.6241	$170.62	$170.60	$170.60
Purchase #4	$38.81	9.620%	$42.5435	$42.54	$42.55	$42.50
Purchase #5	$173.44	5.457%	$182.9046	$182.90	$182.90	$182.90
Purchase #6	$65.37	9.434%	$71.537	$71.54	$71.55	$71.50
Purchase #7	$47.47	7.720%	$51.1347	$51.13	$51.15	$51.10
7 purchase totals =	$906.62		$992.7960	$992.78	$992.80	$992.70