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	$26.67	6.772%	$28.4761	$28.48	$28.50	$28.50
Purchase #2	$200.44	12.841%	$226.1785	$226.18	$226.20	$226.20
Purchase #3	$193.82	3.354%	$200.3207	$200.32	$200.30	$200.30
Purchase #4	$179.47	4.424%	$187.4098	$187.41	$187.40	$187.40
Purchase #5	$68.95	8.504%	$74.8135	$74.81	$74.80	$74.80
Purchase #6	$208.83	4.841%	$218.9395	$218.94	$218.95	$218.90
Purchase #7	$102.87	8.319%	$111.4278	$111.43	$111.45	$111.40
7 purchase totals =	$981.05		$1,047.5659	$1,047.57	$1,047.60	$1,047.50