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	$212.80	8.239%	$230.3326	$230.33	$230.35	$230.30
Purchase #2	$123.25	13.550%	$139.9504	$139.95	$139.95	$140.00
Purchase #3	$86.63	5.749%	$91.6104	$91.61	$91.60	$91.60
Purchase #4	$245.27	9.431%	$268.4014	$268.40	$268.40	$268.40
Purchase #5	$108.28	4.374%	$113.0162	$113.02	$113.00	$113.00
Purchase #6	$35.78	12.182%	$40.1387	$40.14	$40.15	$40.10
Purchase #7	$105.89	12.874%	$119.5223	$119.52	$119.50	$119.50
7 purchase totals =	$917.90		$1,002.9720	$1,002.97	$1,002.95	$1,002.90