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	$30.58	4.383%	$31.9203	$31.92	$31.90	$31.90
Purchase #2	$84.89	4.378%	$88.6065	$88.61	$88.60	$88.60
Purchase #3	$68.54	3.832%	$71.1665	$71.17	$71.15	$71.20
Purchase #4	$153.90	8.123%	$166.4013	$166.40	$166.40	$166.40
Purchase #5	$86.52	13.696%	$98.3698	$98.37	$98.35	$98.40
Purchase #6	$49.33	10.831%	$54.6729	$54.67	$54.65	$54.70
Purchase #7	$47.59	4.105%	$49.5436	$49.54	$49.55	$49.50
7 purchase totals =	$521.35		$560.6809	$560.68	$560.60	$560.70