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	$85.59	3.472%	$88.5617	$88.56	$88.55	$88.60
Purchase #2	$123.54	10.300%	$136.2646	$136.26	$136.25	$136.30
Purchase #3	$80.82	12.295%	$90.7568	$90.76	$90.75	$90.80
Purchase #4	$197.80	8.342%	$214.3005	$214.30	$214.30	$214.30
Purchase #5	$16.73	13.672%	$19.0173	$19.02	$19.00	$19.00
Purchase #6	$58.67	7.124%	$62.8497	$62.85	$62.85	$62.80
Purchase #7	$38.95	10.640%	$43.0943	$43.09	$43.10	$43.10
7 purchase totals =	$602.10		$654.8449	$654.84	$654.80	$654.90