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	$150.39	12.207%	$168.7481	$168.75	$168.75	$168.70
Purchase #2	$125.69	6.233%	$133.5243	$133.52	$133.50	$133.50
Purchase #3	$72.62	7.501%	$78.0672	$78.07	$78.05	$78.10
Purchase #4	$40.26	13.341%	$45.6311	$45.63	$45.65	$45.60
Purchase #5	$165.98	13.525%	$188.4288	$188.43	$188.45	$188.40
Purchase #6	$119.91	7.727%	$129.1754	$129.18	$129.20	$129.20
Purchase #7	$43.82	4.249%	$45.6819	$45.68	$45.70	$45.70
7 purchase totals =	$718.67		$789.2568	$789.26	$789.30	$789.20