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	$26.33	11.862%	$29.4533	$29.45	$29.45	$29.50
Purchase #2	$145.43	3.522%	$150.552	$150.55	$150.55	$150.60
Purchase #3	$98.65	9.574%	$108.0948	$108.09	$108.10	$108.10
Purchase #4	$54.64	13.703%	$62.1273	$62.13	$62.15	$62.10
Purchase #5	$95.75	9.137%	$104.4987	$104.50	$104.50	$104.50
Purchase #6	$41.70	8.469%	$45.2316	$45.23	$45.25	$45.20
Purchase #7	$101.90	6.539%	$108.5632	$108.56	$108.55	$108.60
7 purchase totals =	$564.40		$608.5209	$608.51	$608.55	$608.60