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	$175.89	8.508%	$190.8547	$190.85	$190.85	$190.90
Purchase #2	$193.61	6.283%	$205.7745	$205.77	$205.75	$205.80
Purchase #3	$98.97	13.543%	$112.3735	$112.37	$112.35	$112.40
Purchase #4	$175.46	5.457%	$185.0349	$185.03	$185.05	$185.00
Purchase #5	$76.60	4.209%	$79.8241	$79.82	$79.80	$79.80
Purchase #6	$130.48	10.845%	$144.6306	$144.63	$144.65	$144.60
Purchase #7	$81.49	12.785%	$91.9085	$91.91	$91.90	$91.90
7 purchase totals =	$932.50		$1,010.4008	$1,010.38	$1,010.35	$1,010.40