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	$11.60	8.339%	$12.5673	$12.57	$12.55	$12.60
Purchase #2	$41.26	10.296%	$45.5081	$45.51	$45.50	$45.50
Purchase #3	$174.53	11.768%	$195.0687	$195.07	$195.05	$195.10
Purchase #4	$165.58	10.723%	$183.3351	$183.34	$183.35	$183.30
Purchase #5	$109.64	5.329%	$115.4827	$115.48	$115.50	$115.50
Purchase #6	$78.54	10.643%	$86.899	$86.90	$86.90	$86.90
Purchase #7	$50.69	6.829%	$54.1516	$54.15	$54.15	$54.20
7 purchase totals =	$631.84		$693.0125	$693.02	$693.00	$693.10