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	$71.59	3.615%	$74.178	$74.18	$74.20	$74.20
Purchase #2	$110.43	12.200%	$123.9025	$123.90	$123.90	$123.90
Purchase #3	$58.91	11.774%	$65.8461	$65.85	$65.85	$65.80
Purchase #4	$37.35	7.278%	$40.0683	$40.07	$40.05	$40.10
Purchase #5	$123.39	11.224%	$137.2393	$137.24	$137.25	$137.20
Purchase #6	$144.75	12.695%	$163.126	$163.13	$163.15	$163.10
Purchase #7	$105.84	5.430%	$111.5871	$111.59	$111.60	$111.60
7 purchase totals =	$652.26		$715.9473	$715.96	$716.00	$715.90