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	$51.72	13.313%	$58.6055	$58.61	$58.60	$58.60
Purchase #2	$138.66	6.673%	$147.9128	$147.91	$147.90	$147.90
Purchase #3	$148.96	3.630%	$154.3672	$154.37	$154.35	$154.40
Purchase #4	$115.47	7.303%	$123.9028	$123.90	$123.90	$123.90
Purchase #5	$67.28	11.307%	$74.8873	$74.89	$74.90	$74.90
Purchase #6	$175.58	10.723%	$194.4074	$194.41	$194.40	$194.40
Purchase #7	$77.83	6.292%	$82.7271	$82.73	$82.75	$82.70
7 purchase totals =	$775.50		$836.8101	$836.82	$836.80	$836.80