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	$64.39	12.615%	$72.5128	$72.51	$72.50	$72.50
Purchase #2	$242.46	7.426%	$260.4651	$260.47	$260.45	$260.50
Purchase #3	$94.47	13.761%	$107.47	$107.47	$107.45	$107.50
Purchase #4	$31.99	4.171%	$33.3243	$33.32	$33.30	$33.30
Purchase #5	$31.28	8.572%	$33.9613	$33.96	$33.95	$34.00
Purchase #6	$146.52	10.644%	$162.1156	$162.12	$162.10	$162.10
Purchase #7	$123.63	13.430%	$140.2335	$140.23	$140.25	$140.20
7 purchase totals =	$734.74		$810.0826	$810.08	$810.00	$810.10