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	$55.61	7.586%	$59.8286	$59.83	$59.85	$59.80
Purchase #2	$48.46	8.596%	$52.6256	$52.63	$52.65	$52.60
Purchase #3	$109.81	13.744%	$124.9023	$124.90	$124.90	$124.90
Purchase #4	$42.80	4.613%	$44.7744	$44.77	$44.75	$44.80
Purchase #5	$146.80	12.143%	$164.6259	$164.63	$164.65	$164.60
Purchase #6	$68.42	9.501%	$74.9206	$74.92	$74.90	$74.90
Purchase #7	$36.56	13.303%	$41.4236	$41.42	$41.40	$41.40
7 purchase totals =	$508.46		$563.1010	$563.10	$563.10	$563.00