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	$27.48	13.121%	$31.0857	$31.09	$31.10	$31.10
Purchase #2	$98.60	9.632%	$108.0972	$108.10	$108.10	$108.10
Purchase #3	$125.25	11.247%	$139.3369	$139.34	$139.35	$139.30
Purchase #4	$158.86	9.454%	$173.8786	$173.88	$173.90	$173.90
Purchase #5	$54.40	9.145%	$59.3749	$59.37	$59.35	$59.40
Purchase #6	$146.34	7.689%	$157.5921	$157.59	$157.60	$157.60
Purchase #7	$237.60	13.419%	$269.4835	$269.48	$269.50	$269.50
7 purchase totals =	$848.53		$938.8489	$938.85	$938.90	$938.90