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	$120.35	9.154%	$131.3668	$131.37	$131.35	$131.40
Purchase #2	$105.69	11.692%	$118.0473	$118.05	$118.05	$118.00
Purchase #3	$18.98	4.216%	$19.7802	$19.78	$19.80	$19.80
Purchase #4	$28.64	11.229%	$31.856	$31.86	$31.85	$31.90
Purchase #5	$138.37	10.562%	$152.9846	$152.98	$153.00	$153.00
Purchase #6	$116.83	6.323%	$124.2172	$124.22	$124.20	$124.20
Purchase #7	$249.95	7.511%	$268.7237	$268.72	$268.70	$268.70
7 purchase totals =	$778.81		$846.9758	$846.98	$846.95	$847.00