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	$91.42	13.662%	$103.9098	$103.91	$103.90	$103.90
Purchase #2	$48.69	4.332%	$50.7993	$50.80	$50.80	$50.80
Purchase #3	$210.42	6.316%	$223.7101	$223.71	$223.70	$223.70
Purchase #4	$157.76	9.483%	$172.7204	$172.72	$172.70	$172.70
Purchase #5	$101.73	6.769%	$108.6161	$108.62	$108.60	$108.60
Purchase #6	$118.89	3.738%	$123.3341	$123.33	$123.35	$123.30
Purchase #7	$237.72	12.400%	$267.1973	$267.20	$267.20	$267.20
7 purchase totals =	$966.63		$1,050.2871	$1,050.29	$1,050.25	$1,050.20