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	$128.82	4.171%	$134.1931	$134.19	$134.20	$134.20
Purchase #2	$86.65	3.194%	$89.4176	$89.42	$89.40	$89.40
Purchase #3	$128.42	3.289%	$132.6437	$132.64	$132.65	$132.60
Purchase #4	$7.40	9.211%	$8.0816	$8.08	$8.10	$8.10
Purchase #5	$99.74	9.766%	$109.4806	$109.48	$109.50	$109.50
Purchase #6	$96.69	13.462%	$109.7064	$109.71	$109.70	$109.70
Purchase #7	$93.31	3.786%	$96.8427	$96.84	$96.85	$96.80
7 purchase totals =	$641.03		$680.3657	$680.36	$680.40	$680.30