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	$173.51	3.313%	$179.2584	$179.26	$179.25	$179.30
Purchase #2	$233.89	5.635%	$247.0697	$247.07	$247.05	$247.10
Purchase #3	$129.31	12.578%	$145.5746	$145.57	$145.55	$145.60
Purchase #4	$96.94	13.339%	$109.8708	$109.87	$109.85	$109.90
Purchase #5	$30.64	8.732%	$33.3155	$33.32	$33.30	$33.30
Purchase #6	$139.81	9.764%	$153.461	$153.46	$153.45	$153.50
Purchase #7	$211.92	5.160%	$222.8551	$222.86	$222.85	$222.90
7 purchase totals =	$1,016.02		$1,091.4051	$1,091.41	$1,091.30	$1,091.60