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	$244.33	12.147%	$274.0088	$274.01	$274.00	$274.00
Purchase #2	$207.61	10.506%	$229.4215	$229.42	$229.40	$229.40
Purchase #3	$59.53	9.670%	$65.2866	$65.29	$65.30	$65.30
Purchase #4	$64.74	11.220%	$72.0038	$72.00	$72.00	$72.00
Purchase #5	$125.77	5.235%	$132.3541	$132.35	$132.35	$132.40
Purchase #6	$104.38	4.640%	$109.2232	$109.22	$109.20	$109.20
Purchase #7	$222.29	8.432%	$241.0335	$241.03	$241.05	$241.00
7 purchase totals =	$1,028.65		$1,123.3315	$1,123.32	$1,123.30	$1,123.30