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	$40.72	4.421%	$42.5202	$42.52	$42.50	$42.50
Purchase #2	$223.62	9.297%	$244.41	$244.41	$244.40	$244.40
Purchase #3	$12.98	7.207%	$13.9155	$13.92	$13.90	$13.90
Purchase #4	$248.60	12.221%	$278.9814	$278.98	$279.00	$279.00
Purchase #5	$183.28	7.871%	$197.706	$197.71	$197.70	$197.70
Purchase #6	$206.97	5.620%	$218.6017	$218.60	$218.60	$218.60
Purchase #7	$95.68	4.829%	$100.3004	$100.30	$100.30	$100.30
7 purchase totals =	$1,011.85		$1,096.4352	$1,096.44	$1,096.40	$1,096.40