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	$93.62	9.396%	$102.4165	$102.42	$102.40	$102.40
Purchase #2	$103.80	12.396%	$116.667	$116.67	$116.65	$116.70
Purchase #3	$43.55	3.626%	$45.1291	$45.13	$45.15	$45.10
Purchase #4	$130.73	8.674%	$142.0695	$142.07	$142.05	$142.10
Purchase #5	$120.51	8.435%	$130.675	$130.68	$130.70	$130.70
Purchase #6	$134.61	5.823%	$142.4483	$142.45	$142.45	$142.40
Purchase #7	$133.77	9.483%	$146.4554	$146.46	$146.45	$146.50
7 purchase totals =	$760.59		$825.8608	$825.88	$825.85	$825.90