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	$122.37	11.397%	$136.3165	$136.32	$136.30	$136.30
Purchase #2	$190.77	4.165%	$198.7156	$198.72	$198.70	$198.70
Purchase #3	$109.84	9.196%	$119.9409	$119.94	$119.95	$119.90
Purchase #4	$146.40	10.142%	$161.2479	$161.25	$161.25	$161.20
Purchase #5	$52.56	13.185%	$59.49	$59.49	$59.50	$59.50
Purchase #6	$211.71	7.550%	$227.6941	$227.69	$227.70	$227.70
Purchase #7	$249.39	5.357%	$262.7498	$262.75	$262.75	$262.70
7 purchase totals =	$1,083.04		$1,166.1548	$1,166.16	$1,166.15	$1,166.00