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	$69.98	12.562%	$78.7709	$78.77	$78.75	$78.80
Purchase #2	$173.56	7.402%	$186.4069	$186.41	$186.40	$186.40
Purchase #3	$75.94	13.353%	$86.0803	$86.08	$86.10	$86.10
Purchase #4	$229.75	12.443%	$258.3378	$258.34	$258.35	$258.30
Purchase #5	$35.64	10.392%	$39.3437	$39.34	$39.35	$39.30
Purchase #6	$99.28	4.178%	$103.4279	$103.43	$103.45	$103.40
Purchase #7	$72.58	6.353%	$77.191	$77.19	$77.20	$77.20
7 purchase totals =	$756.73		$829.5585	$829.56	$829.60	$829.50