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	$78.94	12.628%	$88.9085	$88.91	$88.90	$88.90
Purchase #2	$250.89	8.740%	$272.8178	$272.82	$272.80	$272.80
Purchase #3	$34.36	9.318%	$37.5617	$37.56	$37.55	$37.60
Purchase #4	$250.61	8.570%	$272.0873	$272.09	$272.10	$272.10
Purchase #5	$178.34	7.263%	$191.2928	$191.29	$191.30	$191.30
Purchase #6	$117.72	13.488%	$133.5981	$133.60	$133.60	$133.60
Purchase #7	$71.61	5.408%	$75.4827	$75.48	$75.50	$75.50
7 purchase totals =	$982.47		$1,071.7489	$1,071.75	$1,071.75	$1,071.80