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	$87.38	12.228%	$98.0648	$98.06	$98.05	$98.10
Purchase #2	$170.71	11.256%	$189.9251	$189.93	$189.95	$189.90
Purchase #3	$173.77	3.263%	$179.4401	$179.44	$179.45	$179.40
Purchase #4	$111.38	10.610%	$123.1974	$123.20	$123.20	$123.20
Purchase #5	$71.93	9.378%	$78.6756	$78.68	$78.70	$78.70
Purchase #6	$26.27	6.679%	$28.0246	$28.02	$28.00	$28.00
Purchase #7	$96.52	4.553%	$100.9146	$100.91	$100.90	$100.90
7 purchase totals =	$737.96		$798.2422	$798.24	$798.25	$798.20