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	$50.70	8.243%	$54.8792	$54.88	$54.90	$54.90
Purchase #2	$79.27	3.817%	$82.2957	$82.30	$82.30	$82.30
Purchase #3	$241.78	5.644%	$255.4261	$255.43	$255.45	$255.40
Purchase #4	$92.76	3.138%	$95.6708	$95.67	$95.65	$95.70
Purchase #5	$78.54	13.552%	$89.1837	$89.18	$89.20	$89.20
Purchase #6	$147.49	12.485%	$165.9041	$165.90	$165.90	$165.90
Purchase #7	$98.55	12.115%	$110.4893	$110.49	$110.50	$110.50
7 purchase totals =	$789.09		$853.8489	$853.85	$853.90	$853.90