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	$47.44	8.791%	$51.6105	$51.61	$51.60	$51.60
Purchase #2	$74.76	13.738%	$85.0305	$85.03	$85.05	$85.00
Purchase #3	$50.86	9.550%	$55.7171	$55.72	$55.70	$55.70
Purchase #4	$70.50	10.804%	$78.1168	$78.12	$78.10	$78.10
Purchase #5	$232.67	13.135%	$263.2312	$263.23	$263.25	$263.20
Purchase #6	$180.77	5.739%	$191.1444	$191.14	$191.15	$191.10
Purchase #7	$105.52	5.869%	$111.713	$111.71	$111.70	$111.70
7 purchase totals =	$762.52		$836.5635	$836.56	$836.55	$836.40