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	$222.93	12.250%	$250.2389	$250.24	$250.25	$250.20
Purchase #2	$61.50	4.794%	$64.4483	$64.45	$64.45	$64.40
Purchase #3	$18.72	10.799%	$20.7416	$20.74	$20.75	$20.70
Purchase #4	$56.70	3.698%	$58.7968	$58.80	$58.80	$58.80
Purchase #5	$78.56	6.684%	$83.811	$83.81	$83.80	$83.80
Purchase #6	$145.73	10.145%	$160.5143	$160.51	$160.50	$160.50
Purchase #7	$137.38	7.492%	$147.6725	$147.67	$147.65	$147.70
7 purchase totals =	$721.52		$786.2234	$786.22	$786.20	$786.10