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	$59.96	6.229%	$63.6949	$63.69	$63.70	$63.70
Purchase #2	$43.72	4.347%	$45.6205	$45.62	$45.60	$45.60
Purchase #3	$88.45	11.172%	$98.3316	$98.33	$98.35	$98.30
Purchase #4	$104.64	6.188%	$111.1151	$111.12	$111.10	$111.10
Purchase #5	$123.35	3.227%	$127.3305	$127.33	$127.35	$127.30
Purchase #6	$131.34	5.283%	$138.2787	$138.28	$138.30	$138.30
Purchase #7	$79.48	5.434%	$83.7989	$83.80	$83.80	$83.80
7 purchase totals =	$630.94		$668.1702	$668.17	$668.20	$668.10