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	$82.55	9.768%	$90.6135	$90.61	$90.60	$90.60
Purchase #2	$139.62	11.626%	$155.8522	$155.85	$155.85	$155.90
Purchase #3	$18.93	10.231%	$20.8667	$20.87	$20.85	$20.90
Purchase #4	$45.82	7.571%	$49.289	$49.29	$49.30	$49.30
Purchase #5	$117.54	13.621%	$133.5501	$133.55	$133.55	$133.60
Purchase #6	$27.42	12.281%	$30.7875	$30.79	$30.80	$30.80
Purchase #7	$238.27	3.810%	$247.3481	$247.35	$247.35	$247.30
7 purchase totals =	$670.15		$728.3071	$728.31	$728.30	$728.40