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	$73.92	6.104%	$78.4321	$78.43	$78.45	$78.40
Purchase #2	$28.92	13.460%	$32.8126	$32.81	$32.80	$32.80
Purchase #3	$163.83	4.838%	$171.7561	$171.76	$171.75	$171.80
Purchase #4	$167.29	5.365%	$176.2651	$176.27	$176.25	$176.30
Purchase #5	$88.52	8.366%	$95.9256	$95.93	$95.95	$95.90
Purchase #6	$215.84	12.393%	$242.5891	$242.59	$242.60	$242.60
Purchase #7	$31.29	3.623%	$32.4236	$32.42	$32.40	$32.40
7 purchase totals =	$769.61		$830.2042	$830.21	$830.20	$830.20