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	$52.47	12.686%	$59.1263	$59.13	$59.15	$59.10
Purchase #2	$18.31	11.494%	$20.4146	$20.41	$20.40	$20.40
Purchase #3	$37.79	11.645%	$42.1906	$42.19	$42.20	$42.20
Purchase #4	$203.53	7.631%	$219.0614	$219.06	$219.05	$219.10
Purchase #5	$132.57	4.196%	$138.1326	$138.13	$138.15	$138.10
Purchase #6	$210.78	13.222%	$238.6493	$238.65	$238.65	$238.60
Purchase #7	$63.58	5.323%	$66.9644	$66.96	$66.95	$67.00
7 purchase totals =	$719.03		$784.5392	$784.53	$784.55	$784.50