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	$63.80	5.273%	$67.1642	$67.16	$67.15	$67.20
Purchase #2	$104.86	9.268%	$114.5784	$114.58	$114.60	$114.60
Purchase #3	$67.65	6.836%	$72.2746	$72.27	$72.25	$72.30
Purchase #4	$33.32	8.194%	$36.0502	$36.05	$36.05	$36.10
Purchase #5	$141.85	12.422%	$159.4706	$159.47	$159.45	$159.50
Purchase #6	$141.40	13.420%	$160.3759	$160.38	$160.40	$160.40
Purchase #7	$231.78	6.782%	$247.4993	$247.50	$247.50	$247.50
7 purchase totals =	$784.66		$857.4132	$857.41	$857.40	$857.60