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	$52.41	5.453%	$55.2679	$55.27	$55.25	$55.30
Purchase #2	$56.33	8.170%	$60.9322	$60.93	$60.95	$60.90
Purchase #3	$142.36	11.607%	$158.8837	$158.88	$158.90	$158.90
Purchase #4	$176.58	6.232%	$187.5845	$187.58	$187.60	$187.60
Purchase #5	$47.26	12.865%	$53.34	$53.34	$53.35	$53.30
Purchase #6	$229.88	3.592%	$238.1373	$238.14	$238.15	$238.10
Purchase #7	$223.80	9.213%	$244.4187	$244.42	$244.40	$244.40
7 purchase totals =	$928.62		$998.5643	$998.56	$998.60	$998.50