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	$123.85	5.255%	$130.3583	$130.36	$130.35	$130.40
Purchase #2	$88.68	13.715%	$100.8425	$100.84	$100.85	$100.80
Purchase #3	$36.97	10.254%	$40.7609	$40.76	$40.75	$40.80
Purchase #4	$42.28	11.248%	$47.0357	$47.04	$47.05	$47.00
Purchase #5	$145.90	13.431%	$165.4958	$165.50	$165.50	$165.50
Purchase #6	$166.30	12.755%	$187.5116	$187.51	$187.50	$187.50
Purchase #7	$39.73	8.669%	$43.1742	$43.17	$43.15	$43.20
7 purchase totals =	$643.71		$715.1790	$715.18	$715.15	$715.20