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	$95.52	12.106%	$107.0837	$107.08	$107.10	$107.10
Purchase #2	$118.42	11.802%	$132.3959	$132.40	$132.40	$132.40
Purchase #3	$127.73	7.393%	$137.1731	$137.17	$137.15	$137.20
Purchase #4	$106.48	3.107%	$109.7883	$109.79	$109.80	$109.80
Purchase #5	$89.48	9.635%	$98.1014	$98.10	$98.10	$98.10
Purchase #6	$111.33	11.828%	$124.4981	$124.50	$124.50	$124.50
Purchase #7	$30.60	3.271%	$31.6009	$31.60	$31.60	$31.60
7 purchase totals =	$679.56		$740.6414	$740.64	$740.65	$740.70