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	$185.31	6.258%	$196.9067	$196.91	$196.90	$196.90
Purchase #2	$123.31	7.124%	$132.0946	$132.09	$132.10	$132.10
Purchase #3	$169.41	3.516%	$175.3665	$175.37	$175.35	$175.40
Purchase #4	$68.73	7.755%	$74.06	$74.06	$74.05	$74.10
Purchase #5	$15.78	5.173%	$16.5963	$16.60	$16.60	$16.60
Purchase #6	$116.61	11.765%	$130.3292	$130.33	$130.35	$130.30
Purchase #7	$72.51	13.313%	$82.1633	$82.16	$82.15	$82.20
7 purchase totals =	$751.66		$807.5166	$807.52	$807.50	$807.60