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	$148.93	11.145%	$165.5282	$165.53	$165.55	$165.50
Purchase #2	$162.68	6.428%	$173.1371	$173.14	$173.15	$173.10
Purchase #3	$151.85	8.251%	$164.3791	$164.38	$164.40	$164.40
Purchase #4	$250.93	11.687%	$280.2562	$280.26	$280.25	$280.30
Purchase #5	$132.76	5.327%	$139.8321	$139.83	$139.85	$139.80
Purchase #6	$221.31	5.400%	$233.2607	$233.26	$233.25	$233.30
Purchase #7	$142.43	8.161%	$154.0537	$154.05	$154.05	$154.10
7 purchase totals =	$1,210.89		$1,310.4471	$1,310.45	$1,310.50	$1,310.50