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	$54.41	13.126%	$61.5519	$61.55	$61.55	$61.60
Purchase #2	$83.82	7.834%	$90.3865	$90.39	$90.40	$90.40
Purchase #3	$47.92	4.603%	$50.1258	$50.13	$50.15	$50.10
Purchase #4	$142.59	11.652%	$159.2046	$159.20	$159.20	$159.20
Purchase #5	$222.55	7.749%	$239.7954	$239.80	$239.80	$239.80
Purchase #6	$105.30	6.691%	$112.3456	$112.35	$112.35	$112.30
Purchase #7	$62.43	8.407%	$67.6785	$67.68	$67.70	$67.70
7 purchase totals =	$719.02		$781.0883	$781.10	$781.15	$781.10