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	$166.52	10.859%	$184.6024	$184.60	$184.60	$184.60
Purchase #2	$19.82	4.765%	$20.7644	$20.76	$20.75	$20.80
Purchase #3	$180.62	8.659%	$196.2599	$196.26	$196.25	$196.30
Purchase #4	$62.32	5.111%	$65.5052	$65.51	$65.50	$65.50
Purchase #5	$110.27	4.212%	$114.9146	$114.91	$114.90	$114.90
Purchase #6	$217.56	4.173%	$226.6388	$226.64	$226.65	$226.60
Purchase #7	$153.88	5.690%	$162.6358	$162.64	$162.65	$162.60
7 purchase totals =	$910.99		$971.3211	$971.32	$971.30	$971.30