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	$38.91	9.355%	$42.55	$42.55	$42.55	$42.60
Purchase #2	$15.34	11.608%	$17.1207	$17.12	$17.10	$17.10
Purchase #3	$100.58	5.318%	$105.9288	$105.93	$105.95	$105.90
Purchase #4	$203.48	13.692%	$231.3405	$231.34	$231.35	$231.30
Purchase #5	$234.63	10.762%	$259.8809	$259.88	$259.90	$259.90
Purchase #6	$18.85	9.871%	$20.7107	$20.71	$20.70	$20.70
Purchase #7	$26.91	3.478%	$27.8459	$27.85	$27.85	$27.80
7 purchase totals =	$638.70		$705.3775	$705.38	$705.40	$705.30