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	$152.46	13.647%	$173.2662	$173.27	$173.25	$173.30
Purchase #2	$138.47	9.318%	$151.3726	$151.37	$151.35	$151.40
Purchase #3	$174.45	6.296%	$185.4334	$185.43	$185.45	$185.40
Purchase #4	$57.59	5.740%	$60.8957	$60.90	$60.90	$60.90
Purchase #5	$77.56	4.304%	$80.8982	$80.90	$80.90	$80.90
Purchase #6	$25.32	3.778%	$26.2766	$26.28	$26.30	$26.30
Purchase #7	$127.46	10.618%	$140.9937	$140.99	$141.00	$141.00
7 purchase totals =	$753.31		$819.1364	$819.14	$819.15	$819.20