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	$72.46	8.215%	$78.4126	$78.41	$78.40	$78.40
Purchase #2	$85.51	3.253%	$88.2916	$88.29	$88.30	$88.30
Purchase #3	$171.40	8.345%	$185.7033	$185.70	$185.70	$185.70
Purchase #4	$26.28	10.579%	$29.0602	$29.06	$29.05	$29.10
Purchase #5	$234.80	11.603%	$262.0438	$262.04	$262.05	$262.00
Purchase #6	$85.64	11.533%	$95.5169	$95.52	$95.50	$95.50
Purchase #7	$91.59	12.258%	$102.8171	$102.82	$102.80	$102.80
7 purchase totals =	$767.68		$841.8455	$841.84	$841.80	$841.80