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	$80.86	10.346%	$89.2258	$89.23	$89.25	$89.20
Purchase #2	$66.65	3.597%	$69.0474	$69.05	$69.05	$69.00
Purchase #3	$47.57	10.625%	$52.6243	$52.62	$52.60	$52.60
Purchase #4	$122.76	13.612%	$139.4701	$139.47	$139.45	$139.50
Purchase #5	$185.35	12.836%	$209.1415	$209.14	$209.15	$209.10
Purchase #6	$174.30	3.105%	$179.712	$179.71	$179.70	$179.70
Purchase #7	$140.42	3.154%	$144.8488	$144.85	$144.85	$144.80
7 purchase totals =	$817.91		$884.0699	$884.07	$884.05	$883.90