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	$10.98	12.159%	$12.3151	$12.32	$12.30	$12.30
Purchase #2	$250.49	13.868%	$285.228	$285.23	$285.25	$285.20
Purchase #3	$163.32	5.218%	$171.842	$171.84	$171.85	$171.80
Purchase #4	$200.89	13.222%	$227.4517	$227.45	$227.45	$227.50
Purchase #5	$142.32	4.711%	$149.0247	$149.02	$149.00	$149.00
Purchase #6	$25.30	10.720%	$28.0122	$28.01	$28.00	$28.00
Purchase #7	$103.42	3.796%	$107.3458	$107.35	$107.35	$107.30
7 purchase totals =	$896.72		$981.2195	$981.22	$981.20	$981.10