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	$34.90	8.606%	$37.9035	$37.90	$37.90	$37.90
Purchase #2	$86.85	5.263%	$91.4209	$91.42	$91.40	$91.40
Purchase #3	$40.91	13.858%	$46.5793	$46.58	$46.60	$46.60
Purchase #4	$95.65	4.154%	$99.6233	$99.62	$99.60	$99.60
Purchase #5	$50.69	7.650%	$54.5678	$54.57	$54.55	$54.60
Purchase #6	$184.53	5.118%	$193.9742	$193.97	$193.95	$194.00
Purchase #7	$120.33	8.172%	$130.1634	$130.16	$130.15	$130.20
7 purchase totals =	$613.86		$654.2324	$654.22	$654.15	$654.30