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	$40.73	11.720%	$45.5036	$45.50	$45.50	$45.50
Purchase #2	$105.89	7.181%	$113.494	$113.49	$113.50	$113.50
Purchase #3	$44.99	4.203%	$46.8809	$46.88	$46.90	$46.90
Purchase #4	$26.89	12.533%	$30.2601	$30.26	$30.25	$30.30
Purchase #5	$117.93	11.844%	$131.8976	$131.90	$131.90	$131.90
Purchase #6	$193.94	4.839%	$203.3248	$203.32	$203.30	$203.30
Purchase #7	$212.48	7.695%	$228.8303	$228.83	$228.85	$228.80
7 purchase totals =	$742.85		$800.1913	$800.18	$800.20	$800.20