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	$41.94	10.848%	$46.4897	$46.49	$46.50	$46.50
Purchase #2	$189.86	4.481%	$198.3676	$198.37	$198.35	$198.40
Purchase #3	$250.68	10.164%	$276.1591	$276.16	$276.15	$276.20
Purchase #4	$76.89	12.370%	$86.4013	$86.40	$86.40	$86.40
Purchase #5	$29.94	7.766%	$32.2651	$32.27	$32.25	$32.30
Purchase #6	$79.97	4.165%	$83.3008	$83.30	$83.30	$83.30
Purchase #7	$74.71	5.235%	$78.6211	$78.62	$78.60	$78.60
7 purchase totals =	$743.99		$801.6047	$801.61	$801.55	$801.70