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	$80.74	11.115%	$89.7143	$89.71	$89.70	$89.70
Purchase #2	$132.62	8.268%	$143.585	$143.59	$143.60	$143.60
Purchase #3	$155.41	7.762%	$167.4729	$167.47	$167.45	$167.50
Purchase #4	$122.91	13.147%	$139.069	$139.07	$139.05	$139.10
Purchase #5	$72.71	12.633%	$81.8955	$81.90	$81.90	$81.90
Purchase #6	$55.51	3.157%	$57.2625	$57.26	$57.25	$57.30
Purchase #7	$66.76	8.470%	$72.4146	$72.41	$72.40	$72.40
7 purchase totals =	$686.66		$751.4138	$751.41	$751.35	$751.50