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	$243.74	12.121%	$273.2837	$273.28	$273.30	$273.30
Purchase #2	$214.90	12.348%	$241.4359	$241.44	$241.45	$241.40
Purchase #3	$93.28	10.492%	$103.0669	$103.07	$103.05	$103.10
Purchase #4	$105.89	10.853%	$117.3822	$117.38	$117.40	$117.40
Purchase #5	$124.61	7.761%	$134.281	$134.28	$134.30	$134.30
Purchase #6	$53.46	10.689%	$59.1743	$59.17	$59.15	$59.20
Purchase #7	$198.36	13.598%	$225.333	$225.33	$225.35	$225.30
7 purchase totals =	$1,034.24		$1,153.9570	$1,153.95	$1,154.00	$1,154.00