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	$126.46	8.657%	$137.4076	$137.41	$137.40	$137.40
Purchase #2	$146.84	12.219%	$164.7824	$164.78	$164.80	$164.80
Purchase #3	$166.56	8.612%	$180.9041	$180.90	$180.90	$180.90
Purchase #4	$248.46	12.293%	$279.0032	$279.00	$279.00	$279.00
Purchase #5	$146.35	5.278%	$154.0744	$154.07	$154.05	$154.10
Purchase #6	$173.31	8.367%	$187.8108	$187.81	$187.80	$187.80
Purchase #7	$165.58	12.251%	$185.8652	$185.87	$185.85	$185.90
7 purchase totals =	$1,173.56		$1,289.8477	$1,289.84	$1,289.80	$1,289.90