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	$188.56	12.721%	$212.5467	$212.55	$212.55	$212.50
Purchase #2	$89.84	10.518%	$99.2894	$99.29	$99.30	$99.30
Purchase #3	$53.40	5.526%	$56.3509	$56.35	$56.35	$56.40
Purchase #4	$228.27	9.857%	$250.7706	$250.77	$250.75	$250.80
Purchase #5	$53.59	6.591%	$57.1221	$57.12	$57.10	$57.10
Purchase #6	$197.88	8.679%	$215.054	$215.05	$215.05	$215.10
Purchase #7	$141.99	4.321%	$148.1254	$148.13	$148.15	$148.10
7 purchase totals =	$953.53		$1,039.2591	$1,039.26	$1,039.25	$1,039.30