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	$149.33	6.540%	$159.0962	$159.10	$159.10	$159.10
Purchase #2	$71.60	9.163%	$78.1607	$78.16	$78.15	$78.20
Purchase #3	$106.29	11.784%	$118.8152	$118.82	$118.80	$118.80
Purchase #4	$77.85	7.722%	$83.8616	$83.86	$83.85	$83.90
Purchase #5	$212.88	10.475%	$235.1792	$235.18	$235.20	$235.20
Purchase #6	$86.86	5.380%	$91.5331	$91.53	$91.55	$91.50
Purchase #7	$57.88	4.728%	$60.6166	$60.62	$60.60	$60.60
7 purchase totals =	$762.69		$827.2626	$827.27	$827.25	$827.30