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	$126.49	12.613%	$142.4442	$142.44	$142.45	$142.40
Purchase #2	$225.96	7.754%	$243.4809	$243.48	$243.50	$243.50
Purchase #3	$40.71	8.699%	$44.2514	$44.25	$44.25	$44.30
Purchase #4	$80.81	10.700%	$89.4567	$89.46	$89.45	$89.50
Purchase #5	$138.90	13.565%	$157.7418	$157.74	$157.75	$157.70
Purchase #6	$35.69	7.501%	$38.3671	$38.37	$38.35	$38.40
Purchase #7	$64.49	3.563%	$66.7878	$66.79	$66.80	$66.80
7 purchase totals =	$713.05		$782.5299	$782.53	$782.55	$782.60