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	$127.32	8.759%	$138.472	$138.47	$138.45	$138.50
Purchase #2	$6.31	4.809%	$6.6134	$6.61	$6.60	$6.60
Purchase #3	$179.33	3.814%	$186.1696	$186.17	$186.15	$186.20
Purchase #4	$31.92	7.490%	$34.3108	$34.31	$34.30	$34.30
Purchase #5	$92.25	12.146%	$103.4547	$103.45	$103.45	$103.50
Purchase #6	$244.41	7.841%	$263.5742	$263.57	$263.55	$263.60
Purchase #7	$72.69	10.381%	$80.2359	$80.24	$80.25	$80.20
7 purchase totals =	$754.23		$812.8306	$812.82	$812.75	$812.90