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	$243.59	8.599%	$264.5363	$264.54	$264.55	$264.50
Purchase #2	$228.76	9.391%	$250.2429	$250.24	$250.25	$250.20
Purchase #3	$97.45	3.191%	$100.5596	$100.56	$100.55	$100.60
Purchase #4	$138.73	10.599%	$153.434	$153.43	$153.45	$153.40
Purchase #5	$171.69	8.577%	$186.4159	$186.42	$186.40	$186.40
Purchase #6	$140.92	3.824%	$146.3088	$146.31	$146.30	$146.30
Purchase #7	$109.44	6.367%	$116.408	$116.41	$116.40	$116.40
7 purchase totals =	$1,130.58		$1,217.9055	$1,217.91	$1,217.90	$1,217.80