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	$216.75	3.117%	$223.5061	$223.51	$223.50	$223.50
Purchase #2	$61.40	11.636%	$68.5445	$68.54	$68.55	$68.50
Purchase #3	$85.38	6.466%	$90.9007	$90.90	$90.90	$90.90
Purchase #4	$54.55	12.703%	$61.4795	$61.48	$61.50	$61.50
Purchase #5	$70.86	13.277%	$80.2681	$80.27	$80.25	$80.30
Purchase #6	$188.95	12.851%	$213.232	$213.23	$213.25	$213.20
Purchase #7	$30.94	10.673%	$34.2422	$34.24	$34.25	$34.20
7 purchase totals =	$708.83		$772.1731	$772.17	$772.20	$772.10