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	$11.90	11.610%	$13.2816	$13.28	$13.30	$13.30
Purchase #2	$70.43	12.844%	$79.476	$79.48	$79.50	$79.50
Purchase #3	$139.38	12.865%	$157.3112	$157.31	$157.30	$157.30
Purchase #4	$39.34	7.763%	$42.394	$42.39	$42.40	$42.40
Purchase #5	$229.50	13.231%	$259.8651	$259.87	$259.85	$259.90
Purchase #6	$221.85	4.549%	$231.942	$231.94	$231.95	$231.90
Purchase #7	$94.60	9.123%	$103.2304	$103.23	$103.25	$103.20
7 purchase totals =	$807.00		$887.5003	$887.50	$887.55	$887.50