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	$79.47	3.730%	$82.4342	$82.43	$82.45	$82.40
Purchase #2	$147.34	10.112%	$162.239	$162.24	$162.25	$162.20
Purchase #3	$57.83	7.326%	$62.0666	$62.07	$62.05	$62.10
Purchase #4	$82.83	3.465%	$85.7001	$85.70	$85.70	$85.70
Purchase #5	$161.41	12.513%	$181.6072	$181.61	$181.60	$181.60
Purchase #6	$240.91	6.771%	$257.222	$257.22	$257.20	$257.20
Purchase #7	$49.35	11.215%	$54.8846	$54.88	$54.90	$54.90
7 purchase totals =	$819.14		$886.1537	$886.15	$886.15	$886.10