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	$76.98	13.433%	$87.3207	$87.32	$87.30	$87.30
Purchase #2	$210.34	11.172%	$233.8392	$233.84	$233.85	$233.80
Purchase #3	$86.76	4.378%	$90.5584	$90.56	$90.55	$90.60
Purchase #4	$68.69	12.347%	$77.1712	$77.17	$77.15	$77.20
Purchase #5	$188.36	4.406%	$196.6591	$196.66	$196.65	$196.70
Purchase #6	$104.58	4.642%	$109.4346	$109.43	$109.45	$109.40
Purchase #7	$34.85	12.656%	$39.2606	$39.26	$39.25	$39.30
7 purchase totals =	$770.56		$834.2438	$834.24	$834.20	$834.30