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	$45.52	11.829%	$50.9046	$50.90	$50.90	$50.90
Purchase #2	$87.52	4.142%	$91.1451	$91.15	$91.15	$91.10
Purchase #3	$26.36	8.772%	$28.6723	$28.67	$28.65	$28.70
Purchase #4	$142.72	5.243%	$150.2028	$150.20	$150.20	$150.20
Purchase #5	$64.58	12.423%	$72.6028	$72.60	$72.60	$72.60
Purchase #6	$31.89	6.108%	$33.8378	$33.84	$33.85	$33.80
Purchase #7	$184.27	7.842%	$198.7205	$198.72	$198.70	$198.70
7 purchase totals =	$582.86		$626.0859	$626.08	$626.05	$626.00