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	$66.57	11.310%	$74.0991	$74.10	$74.10	$74.10
Purchase #2	$86.79	6.284%	$92.2439	$92.24	$92.25	$92.20
Purchase #3	$40.63	13.782%	$46.2296	$46.23	$46.25	$46.20
Purchase #4	$136.53	12.580%	$153.7055	$153.71	$153.70	$153.70
Purchase #5	$72.97	10.850%	$80.8872	$80.89	$80.90	$80.90
Purchase #6	$100.25	11.205%	$111.483	$111.48	$111.50	$111.50
Purchase #7	$20.63	4.828%	$21.626	$21.63	$21.65	$21.60
7 purchase totals =	$524.37		$580.2743	$580.28	$580.35	$580.20