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	$52.68	13.406%	$59.7423	$59.74	$59.75	$59.70
Purchase #2	$197.68	10.570%	$218.5748	$218.57	$218.55	$218.60
Purchase #3	$85.90	12.484%	$96.6238	$96.62	$96.60	$96.60
Purchase #4	$35.95	4.217%	$37.466	$37.47	$37.45	$37.50
Purchase #5	$135.31	4.460%	$141.3448	$141.34	$141.35	$141.30
Purchase #6	$20.31	5.453%	$21.4175	$21.42	$21.40	$21.40
Purchase #7	$87.57	8.671%	$95.1632	$95.16	$95.15	$95.20
7 purchase totals =	$615.40		$670.3324	$670.32	$670.25	$670.30