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	$83.69	7.519%	$89.9827	$89.98	$90.00	$90.00
Purchase #2	$14.45	13.839%	$16.4497	$16.45	$16.45	$16.40
Purchase #3	$241.90	8.531%	$262.5365	$262.54	$262.55	$262.50
Purchase #4	$108.89	13.231%	$123.2972	$123.30	$123.30	$123.30
Purchase #5	$246.32	4.761%	$258.0473	$258.05	$258.05	$258.00
Purchase #6	$242.26	4.779%	$253.8376	$253.84	$253.85	$253.80
Purchase #7	$169.30	12.854%	$191.0618	$191.06	$191.05	$191.10
7 purchase totals =	$1,106.81		$1,195.2128	$1,195.22	$1,195.25	$1,195.10