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	$42.41	11.612%	$47.3346	$47.33	$47.35	$47.30
Purchase #2	$190.93	10.166%	$210.3399	$210.34	$210.35	$210.30
Purchase #3	$106.52	13.326%	$120.7149	$120.71	$120.70	$120.70
Purchase #4	$133.42	11.309%	$148.5085	$148.51	$148.50	$148.50
Purchase #5	$76.74	12.233%	$86.1276	$86.13	$86.15	$86.10
Purchase #6	$101.25	3.796%	$105.0935	$105.09	$105.10	$105.10
Purchase #7	$211.71	12.853%	$238.9211	$238.92	$238.90	$238.90
7 purchase totals =	$862.98		$957.0401	$957.03	$957.05	$956.90