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	$215.28	3.841%	$223.5489	$223.55	$223.55	$223.50
Purchase #2	$111.91	5.725%	$118.3168	$118.32	$118.30	$118.30
Purchase #3	$185.27	12.728%	$208.8512	$208.85	$208.85	$208.90
Purchase #4	$21.73	6.460%	$23.1338	$23.13	$23.15	$23.10
Purchase #5	$92.98	8.150%	$100.5579	$100.56	$100.55	$100.60
Purchase #6	$214.72	4.659%	$224.7238	$224.72	$224.70	$224.70
Purchase #7	$168.26	6.850%	$179.7858	$179.79	$179.80	$179.80
7 purchase totals =	$1,010.15		$1,078.9182	$1,078.92	$1,078.90	$1,078.90