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	$20.64	4.272%	$21.5217	$21.52	$21.50	$21.50
Purchase #2	$83.72	5.163%	$88.0425	$88.04	$88.05	$88.00
Purchase #3	$27.70	4.142%	$28.8473	$28.85	$28.85	$28.80
Purchase #4	$171.53	10.640%	$189.7808	$189.78	$189.80	$189.80
Purchase #5	$233.42	12.431%	$262.4364	$262.44	$262.45	$262.40
Purchase #6	$127.66	4.134%	$132.9375	$132.94	$132.95	$132.90
Purchase #7	$101.70	13.821%	$115.756	$115.76	$115.75	$115.80
7 purchase totals =	$766.37		$839.3222	$839.33	$839.35	$839.20