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	$34.45	7.594%	$37.0661	$37.07	$37.05	$37.10
Purchase #2	$96.41	6.337%	$102.5195	$102.52	$102.50	$102.50
Purchase #3	$194.80	7.610%	$209.6243	$209.62	$209.60	$209.60
Purchase #4	$194.38	10.381%	$214.5586	$214.56	$214.55	$214.60
Purchase #5	$56.55	10.562%	$62.5228	$62.52	$62.50	$62.50
Purchase #6	$119.82	11.324%	$133.3884	$133.39	$133.40	$133.40
Purchase #7	$98.64	12.648%	$111.116	$111.12	$111.10	$111.10
7 purchase totals =	$795.05		$870.7957	$870.80	$870.70	$870.80