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	$19.53	13.392%	$22.1455	$22.15	$22.15	$22.10
Purchase #2	$57.66	11.457%	$64.2661	$64.27	$64.25	$64.30
Purchase #3	$93.91	10.110%	$103.4043	$103.40	$103.40	$103.40
Purchase #4	$125.43	13.119%	$141.8852	$141.89	$141.90	$141.90
Purchase #5	$182.40	10.124%	$200.8662	$200.87	$200.85	$200.90
Purchase #6	$106.83	11.546%	$119.1646	$119.16	$119.15	$119.20
Purchase #7	$55.68	3.813%	$57.8031	$57.80	$57.80	$57.80
7 purchase totals =	$641.44		$709.5350	$709.54	$709.50	$709.60