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	$216.71	9.409%	$237.1002	$237.10	$237.10	$237.10
Purchase #2	$100.51	9.115%	$109.6715	$109.67	$109.65	$109.70
Purchase #3	$64.33	3.326%	$66.4696	$66.47	$66.45	$66.50
Purchase #4	$121.42	6.169%	$128.9104	$128.91	$128.90	$128.90
Purchase #5	$115.62	13.502%	$131.231	$131.23	$131.25	$131.20
Purchase #6	$159.61	8.313%	$172.8784	$172.88	$172.90	$172.90
Purchase #7	$216.46	12.293%	$243.0694	$243.07	$243.05	$243.10
7 purchase totals =	$994.66		$1,089.3305	$1,089.33	$1,089.30	$1,089.40