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	$99.31	13.175%	$112.3941	$112.39	$112.40	$112.40
Purchase #2	$78.46	10.135%	$86.4119	$86.41	$86.40	$86.40
Purchase #3	$138.49	11.469%	$154.3734	$154.37	$154.35	$154.40
Purchase #4	$92.84	9.796%	$101.9346	$101.93	$101.95	$101.90
Purchase #5	$163.32	12.726%	$184.1041	$184.10	$184.10	$184.10
Purchase #6	$34.82	6.713%	$37.1575	$37.16	$37.15	$37.20
Purchase #7	$129.54	7.498%	$139.2529	$139.25	$139.25	$139.30
7 purchase totals =	$736.78		$815.6285	$815.61	$815.60	$815.70