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	$74.26	9.519%	$81.3288	$81.33	$81.35	$81.30
Purchase #2	$160.45	11.764%	$179.3253	$179.33	$179.35	$179.30
Purchase #3	$201.27	4.136%	$209.5945	$209.59	$209.60	$209.60
Purchase #4	$11.83	3.613%	$12.2574	$12.26	$12.25	$12.30
Purchase #5	$211.62	12.518%	$238.1106	$238.11	$238.10	$238.10
Purchase #6	$76.31	8.719%	$82.9635	$82.96	$82.95	$83.00
Purchase #7	$59.44	5.754%	$62.8602	$62.86	$62.85	$62.90
7 purchase totals =	$795.18		$866.4403	$866.44	$866.45	$866.50