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	$131.75	10.764%	$145.9316	$145.93	$145.95	$145.90
Purchase #2	$96.94	3.499%	$100.3319	$100.33	$100.35	$100.30
Purchase #3	$88.33	9.495%	$96.7169	$96.72	$96.70	$96.70
Purchase #4	$29.94	13.495%	$33.9804	$33.98	$34.00	$34.00
Purchase #5	$172.45	5.251%	$181.5053	$181.51	$181.50	$181.50
Purchase #6	$112.55	3.704%	$116.7189	$116.72	$116.70	$116.70
Purchase #7	$92.78	13.128%	$104.9602	$104.96	$104.95	$105.00
7 purchase totals =	$724.74		$780.1452	$780.15	$780.15	$780.10