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	$233.44	3.845%	$242.4158	$242.42	$242.40	$242.40
Purchase #2	$223.52	13.850%	$254.4775	$254.48	$254.50	$254.50
Purchase #3	$113.54	12.396%	$127.6144	$127.61	$127.60	$127.60
Purchase #4	$190.80	9.730%	$209.3648	$209.36	$209.35	$209.40
Purchase #5	$29.95	13.122%	$33.88	$33.88	$33.90	$33.90
Purchase #6	$143.94	3.105%	$148.4093	$148.41	$148.40	$148.40
Purchase #7	$124.75	13.216%	$141.237	$141.24	$141.25	$141.20
7 purchase totals =	$1,059.94		$1,157.3988	$1,157.40	$1,157.40	$1,157.40