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	$170.79	13.536%	$193.9081	$193.91	$193.90	$193.90
Purchase #2	$127.98	3.607%	$132.5962	$132.60	$132.60	$132.60
Purchase #3	$37.98	11.800%	$42.4616	$42.46	$42.45	$42.50
Purchase #4	$121.69	12.779%	$137.2408	$137.24	$137.25	$137.20
Purchase #5	$86.62	13.834%	$98.603	$98.60	$98.60	$98.60
Purchase #6	$215.77	7.788%	$232.5742	$232.57	$232.55	$232.60
Purchase #7	$72.98	5.663%	$77.1129	$77.11	$77.10	$77.10
7 purchase totals =	$833.81		$914.4968	$914.49	$914.45	$914.50