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	$30.27	6.642%	$32.2805	$32.28	$32.30	$32.30
Purchase #2	$153.67	5.341%	$161.8775	$161.88	$161.90	$161.90
Purchase #3	$128.91	11.844%	$144.1781	$144.18	$144.20	$144.20
Purchase #4	$241.50	9.548%	$264.5584	$264.56	$264.55	$264.60
Purchase #5	$147.33	12.546%	$165.814	$165.81	$165.80	$165.80
Purchase #6	$64.44	12.157%	$72.274	$72.27	$72.25	$72.30
Purchase #7	$126.41	10.380%	$139.5314	$139.53	$139.55	$139.50
7 purchase totals =	$892.53		$980.5139	$980.51	$980.55	$980.60