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	$158.39	7.874%	$170.8616	$170.86	$170.85	$170.90
Purchase #2	$5.85	6.373%	$6.2228	$6.22	$6.20	$6.20
Purchase #3	$196.92	10.371%	$217.3426	$217.34	$217.35	$217.30
Purchase #4	$60.69	7.317%	$65.1307	$65.13	$65.15	$65.10
Purchase #5	$132.72	7.387%	$142.524	$142.52	$142.50	$142.50
Purchase #6	$124.53	9.826%	$136.7663	$136.77	$136.75	$136.80
Purchase #7	$54.55	13.427%	$61.8744	$61.87	$61.85	$61.90
7 purchase totals =	$733.65		$800.7224	$800.71	$800.65	$800.70