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	$231.53	3.435%	$239.4831	$239.48	$239.50	$239.50
Purchase #2	$58.46	9.335%	$63.9172	$63.92	$63.90	$63.90
Purchase #3	$120.42	6.105%	$127.7716	$127.77	$127.75	$127.80
Purchase #4	$80.98	7.163%	$86.7806	$86.78	$86.80	$86.80
Purchase #5	$218.27	4.535%	$228.1685	$228.17	$228.15	$228.20
Purchase #6	$159.89	11.409%	$178.1319	$178.13	$178.15	$178.10
Purchase #7	$196.81	13.835%	$224.0387	$224.04	$224.05	$224.00
7 purchase totals =	$1,066.36		$1,148.2916	$1,148.29	$1,148.30	$1,148.30