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	$119.26	3.470%	$123.3983	$123.40	$123.40	$123.40
Purchase #2	$91.67	9.866%	$100.7142	$100.71	$100.70	$100.70
Purchase #3	$82.78	7.482%	$88.9736	$88.97	$88.95	$89.00
Purchase #4	$152.66	3.775%	$158.4229	$158.42	$158.40	$158.40
Purchase #5	$31.38	4.650%	$32.8392	$32.84	$32.85	$32.80
Purchase #6	$96.65	3.542%	$100.0733	$100.07	$100.05	$100.10
Purchase #7	$228.97	6.353%	$243.5165	$243.52	$243.50	$243.50
7 purchase totals =	$803.37		$847.9380	$847.93	$847.85	$847.90