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	$34.43	8.679%	$37.4182	$37.42	$37.40	$37.40
Purchase #2	$120.35	6.160%	$127.7636	$127.76	$127.75	$127.80
Purchase #3	$109.67	12.553%	$123.4369	$123.44	$123.45	$123.40
Purchase #4	$26.69	8.142%	$28.8631	$28.86	$28.85	$28.90
Purchase #5	$98.37	4.772%	$103.0642	$103.06	$103.05	$103.10
Purchase #6	$215.82	6.388%	$229.6066	$229.61	$229.60	$229.60
Purchase #7	$236.28	12.179%	$265.0565	$265.06	$265.05	$265.10
7 purchase totals =	$841.61		$915.2091	$915.21	$915.15	$915.30