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	$31.73	10.157%	$34.9528	$34.95	$34.95	$35.00
Purchase #2	$129.45	13.317%	$146.6889	$146.69	$146.70	$146.70
Purchase #3	$24.86	11.845%	$27.8047	$27.80	$27.80	$27.80
Purchase #4	$82.96	7.815%	$89.4433	$89.44	$89.45	$89.40
Purchase #5	$134.71	5.722%	$142.4181	$142.42	$142.40	$142.40
Purchase #6	$170.55	8.542%	$185.1184	$185.12	$185.10	$185.10
Purchase #7	$153.63	12.700%	$173.141	$173.14	$173.15	$173.10
7 purchase totals =	$727.89		$799.5672	$799.56	$799.55	$799.50