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	$126.78	3.230%	$130.875	$130.88	$130.90	$130.90
Purchase #2	$211.70	5.471%	$223.2821	$223.28	$223.30	$223.30
Purchase #3	$197.96	5.150%	$208.1549	$208.15	$208.15	$208.20
Purchase #4	$44.68	6.695%	$47.6713	$47.67	$47.65	$47.70
Purchase #5	$78.38	4.777%	$82.1242	$82.12	$82.10	$82.10
Purchase #6	$101.51	9.411%	$111.0631	$111.06	$111.05	$111.10
Purchase #7	$164.46	8.557%	$178.5328	$178.53	$178.55	$178.50
7 purchase totals =	$925.47		$981.7034	$981.69	$981.70	$981.80