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	$158.63	13.740%	$180.4258	$180.43	$180.45	$180.40
Purchase #2	$250.73	5.370%	$264.1942	$264.19	$264.20	$264.20
Purchase #3	$48.72	5.261%	$51.2832	$51.28	$51.30	$51.30
Purchase #4	$126.53	3.462%	$130.9105	$130.91	$130.90	$130.90
Purchase #5	$174.42	5.128%	$183.3643	$183.36	$183.35	$183.40
Purchase #6	$115.66	11.158%	$128.5653	$128.57	$128.55	$128.60
Purchase #7	$56.89	4.253%	$59.3095	$59.31	$59.30	$59.30
7 purchase totals =	$931.58		$998.0528	$998.05	$998.05	$998.10