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	$111.32	6.283%	$118.3142	$118.31	$118.30	$118.30
Purchase #2	$203.54	10.212%	$224.3255	$224.33	$224.35	$224.30
Purchase #3	$78.38	5.376%	$82.5937	$82.59	$82.60	$82.60
Purchase #4	$13.70	8.805%	$14.9063	$14.91	$14.90	$14.90
Purchase #5	$10.44	11.719%	$11.6635	$11.66	$11.65	$11.70
Purchase #6	$88.36	12.403%	$99.3193	$99.32	$99.30	$99.30
Purchase #7	$94.79	3.452%	$98.0622	$98.06	$98.05	$98.10
7 purchase totals =	$600.53		$649.1847	$649.18	$649.15	$649.20