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	$34.48	9.193%	$37.6497	$37.65	$37.65	$37.60
Purchase #2	$116.84	3.816%	$121.2986	$121.30	$121.30	$121.30
Purchase #3	$5.39	12.540%	$6.0659	$6.07	$6.05	$6.10
Purchase #4	$68.40	4.656%	$71.5847	$71.58	$71.60	$71.60
Purchase #5	$94.98	6.172%	$100.8422	$100.84	$100.85	$100.80
Purchase #6	$211.96	6.799%	$226.3712	$226.37	$226.35	$226.40
Purchase #7	$95.55	5.475%	$100.7814	$100.78	$100.80	$100.80
7 purchase totals =	$627.60		$664.5937	$664.59	$664.60	$664.60