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	$117.88	9.105%	$128.613	$128.61	$128.60	$128.60
Purchase #2	$166.56	11.282%	$185.3513	$185.35	$185.35	$185.40
Purchase #3	$90.46	11.515%	$100.8765	$100.88	$100.90	$100.90
Purchase #4	$80.70	6.832%	$86.2134	$86.21	$86.20	$86.20
Purchase #5	$140.86	13.188%	$159.4366	$159.44	$159.45	$159.40
Purchase #6	$72.53	4.807%	$76.0165	$76.02	$76.00	$76.00
Purchase #7	$110.96	7.476%	$119.2554	$119.26	$119.25	$119.30
7 purchase totals =	$779.95		$855.7627	$855.77	$855.75	$855.80