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	$63.81	12.282%	$71.6471	$71.65	$71.65	$71.60
Purchase #2	$49.80	12.158%	$55.8547	$55.85	$55.85	$55.90
Purchase #3	$50.83	10.595%	$56.2154	$56.22	$56.20	$56.20
Purchase #4	$42.58	6.619%	$45.3984	$45.40	$45.40	$45.40
Purchase #5	$190.88	10.387%	$210.7067	$210.71	$210.70	$210.70
Purchase #6	$126.97	10.176%	$139.8905	$139.89	$139.90	$139.90
Purchase #7	$20.33	8.361%	$22.0298	$22.03	$22.05	$22.00
7 purchase totals =	$545.20		$601.7426	$601.75	$601.75	$601.70