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	$31.40	8.465%	$34.058	$34.06	$34.05	$34.10
Purchase #2	$89.74	4.785%	$94.0341	$94.03	$94.05	$94.00
Purchase #3	$19.27	6.404%	$20.5041	$20.50	$20.50	$20.50
Purchase #4	$80.64	10.821%	$89.3661	$89.37	$89.35	$89.40
Purchase #5	$138.48	4.340%	$144.49	$144.49	$144.50	$144.50
Purchase #6	$52.91	10.411%	$58.4185	$58.42	$58.40	$58.40
Purchase #7	$89.33	13.439%	$101.3351	$101.34	$101.35	$101.30
7 purchase totals =	$501.77		$542.2059	$542.21	$542.20	$542.20