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	$150.54	13.675%	$171.1263	$171.13	$171.15	$171.10
Purchase #2	$77.96	5.522%	$82.265	$82.27	$82.25	$82.30
Purchase #3	$243.67	13.361%	$276.2267	$276.23	$276.25	$276.20
Purchase #4	$6.45	9.454%	$7.0598	$7.06	$7.05	$7.10
Purchase #5	$152.86	13.459%	$173.4334	$173.43	$173.45	$173.40
Purchase #6	$242.85	13.518%	$275.6785	$275.68	$275.70	$275.70
Purchase #7	$15.69	4.868%	$16.4538	$16.45	$16.45	$16.50
7 purchase totals =	$890.02		$1,002.2435	$1,002.25	$1,002.30	$1,002.30