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	$136.56	9.439%	$149.4499	$149.45	$149.45	$149.40
Purchase #2	$99.38	7.585%	$106.918	$106.92	$106.90	$106.90
Purchase #3	$46.73	7.795%	$50.3726	$50.37	$50.35	$50.40
Purchase #4	$89.83	12.307%	$100.8854	$100.89	$100.90	$100.90
Purchase #5	$129.75	8.594%	$140.9007	$140.90	$140.90	$140.90
Purchase #6	$49.92	12.419%	$56.1196	$56.12	$56.10	$56.10
Purchase #7	$48.37	13.541%	$54.9198	$54.92	$54.90	$54.90
7 purchase totals =	$600.54		$659.5660	$659.57	$659.50	$659.50