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	$85.30	8.755%	$92.768	$92.77	$92.75	$92.80
Purchase #2	$246.62	13.261%	$279.3243	$279.32	$279.30	$279.30
Purchase #3	$209.77	5.866%	$222.0751	$222.08	$222.10	$222.10
Purchase #4	$97.89	6.769%	$104.5162	$104.52	$104.50	$104.50
Purchase #5	$229.31	10.617%	$253.6558	$253.66	$253.65	$253.70
Purchase #6	$114.36	4.469%	$119.4707	$119.47	$119.45	$119.50
Purchase #7	$115.66	3.638%	$119.8677	$119.87	$119.85	$119.90
7 purchase totals =	$1,098.91		$1,191.6778	$1,191.69	$1,191.60	$1,191.80