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	$54.61	7.149%	$58.5141	$58.51	$58.50	$58.50
Purchase #2	$233.56	5.271%	$245.8709	$245.87	$245.85	$245.90
Purchase #3	$142.60	8.814%	$155.1688	$155.17	$155.15	$155.20
Purchase #4	$117.38	11.236%	$130.5688	$130.57	$130.55	$130.60
Purchase #5	$117.93	10.870%	$130.749	$130.75	$130.75	$130.70
Purchase #6	$30.52	10.829%	$33.825	$33.83	$33.85	$33.80
Purchase #7	$82.50	11.119%	$91.6732	$91.67	$91.65	$91.70
7 purchase totals =	$779.10		$846.3698	$846.37	$846.30	$846.40