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	$50.49	6.299%	$53.6704	$53.67	$53.65	$53.70
Purchase #2	$34.90	8.593%	$37.899	$37.90	$37.90	$37.90
Purchase #3	$42.39	7.610%	$45.6159	$45.62	$45.60	$45.60
Purchase #4	$223.78	7.831%	$241.3042	$241.30	$241.30	$241.30
Purchase #5	$86.94	13.849%	$98.9803	$98.98	$99.00	$99.00
Purchase #6	$168.54	6.671%	$179.7833	$179.78	$179.80	$179.80
Purchase #7	$31.75	3.813%	$32.9606	$32.96	$32.95	$33.00
7 purchase totals =	$638.79		$690.2137	$690.21	$690.20	$690.30