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	$26.97	13.745%	$30.677	$30.68	$30.70	$30.70
Purchase #2	$181.38	13.155%	$205.2405	$205.24	$205.25	$205.20
Purchase #3	$230.89	8.447%	$250.3933	$250.39	$250.40	$250.40
Purchase #4	$7.64	3.227%	$7.8865	$7.89	$7.90	$7.90
Purchase #5	$218.42	10.119%	$240.5219	$240.52	$240.50	$240.50
Purchase #6	$89.72	3.155%	$92.5507	$92.55	$92.55	$92.60
Purchase #7	$49.75	4.293%	$51.8858	$51.89	$51.90	$51.90
7 purchase totals =	$804.77		$879.1557	$879.16	$879.20	$879.20