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	$80.89	6.217%	$85.9189	$85.92	$85.90	$85.90
Purchase #2	$221.82	9.317%	$242.487	$242.49	$242.50	$242.50
Purchase #3	$243.35	5.821%	$257.5154	$257.52	$257.50	$257.50
Purchase #4	$105.91	6.159%	$112.433	$112.43	$112.45	$112.40
Purchase #5	$105.66	13.200%	$119.6071	$119.61	$119.60	$119.60
Purchase #6	$222.25	3.401%	$229.8087	$229.81	$229.80	$229.80
Purchase #7	$201.94	10.115%	$222.3662	$222.37	$222.35	$222.40
7 purchase totals =	$1,181.82		$1,270.1363	$1,270.15	$1,270.10	$1,270.10