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	$39.61	13.814%	$45.0817	$45.08	$45.10	$45.10
Purchase #2	$69.59	11.387%	$77.5142	$77.51	$77.50	$77.50
Purchase #3	$218.75	7.180%	$234.4563	$234.46	$234.45	$234.50
Purchase #4	$84.58	6.372%	$89.9694	$89.97	$89.95	$90.00
Purchase #5	$73.74	10.219%	$81.2755	$81.28	$81.30	$81.30
Purchase #6	$56.37	10.311%	$62.1823	$62.18	$62.20	$62.20
Purchase #7	$10.89	3.823%	$11.3063	$11.31	$11.30	$11.30
7 purchase totals =	$553.53		$601.7857	$601.79	$601.80	$601.90