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	$241.76	13.261%	$273.8198	$273.82	$273.80	$273.80
Purchase #2	$100.81	11.548%	$112.4515	$112.45	$112.45	$112.50
Purchase #3	$158.90	4.225%	$165.6135	$165.61	$165.60	$165.60
Purchase #4	$60.48	9.830%	$66.4252	$66.43	$66.45	$66.40
Purchase #5	$73.82	7.217%	$79.1476	$79.15	$79.15	$79.10
Purchase #6	$60.80	6.196%	$64.5672	$64.57	$64.55	$64.60
Purchase #7	$186.62	3.351%	$192.8736	$192.87	$192.85	$192.90
7 purchase totals =	$883.19		$954.8984	$954.90	$954.85	$954.90