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	$205.65	12.772%	$231.9156	$231.92	$231.90	$231.90
Purchase #2	$216.81	12.285%	$243.4451	$243.45	$243.45	$243.40
Purchase #3	$169.28	12.291%	$190.0862	$190.09	$190.10	$190.10
Purchase #4	$179.28	10.737%	$198.5293	$198.53	$198.55	$198.50
Purchase #5	$247.62	12.280%	$278.0277	$278.03	$278.05	$278.00
Purchase #6	$89.61	10.797%	$99.2852	$99.29	$99.30	$99.30
Purchase #7	$10.91	10.195%	$12.0223	$12.02	$12.00	$12.00
7 purchase totals =	$1,119.16		$1,253.3114	$1,253.33	$1,253.35	$1,253.20