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	$107.35	10.346%	$118.4564	$118.46	$118.45	$118.50
Purchase #2	$64.96	9.431%	$71.0864	$71.09	$71.10	$71.10
Purchase #3	$195.45	12.347%	$219.5822	$219.58	$219.60	$219.60
Purchase #4	$90.55	9.676%	$99.3116	$99.31	$99.30	$99.30
Purchase #5	$17.77	7.455%	$19.0948	$19.09	$19.10	$19.10
Purchase #6	$91.62	7.487%	$98.4796	$98.48	$98.50	$98.50
Purchase #7	$189.30	13.635%	$215.1111	$215.11	$215.10	$215.10
7 purchase totals =	$757.00		$841.1221	$841.12	$841.15	$841.20