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	$139.37	12.409%	$156.6644	$156.66	$156.65	$156.70
Purchase #2	$151.82	7.299%	$162.9013	$162.90	$162.90	$162.90
Purchase #3	$88.89	3.454%	$91.9603	$91.96	$91.95	$92.00
Purchase #4	$158.63	11.259%	$176.4902	$176.49	$176.50	$176.50
Purchase #5	$66.91	4.787%	$70.113	$70.11	$70.10	$70.10
Purchase #6	$205.36	6.419%	$218.5421	$218.54	$218.55	$218.50
Purchase #7	$18.89	13.863%	$21.5087	$21.51	$21.50	$21.50
7 purchase totals =	$829.87		$898.1800	$898.17	$898.15	$898.20