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	$10.39	10.441%	$11.4748	$11.47	$11.45	$11.50
Purchase #2	$140.47	5.649%	$148.4052	$148.41	$148.40	$148.40
Purchase #3	$81.69	4.632%	$85.4739	$85.47	$85.45	$85.50
Purchase #4	$90.28	6.464%	$96.1157	$96.12	$96.10	$96.10
Purchase #5	$226.37	7.586%	$243.5424	$243.54	$243.55	$243.50
Purchase #6	$24.32	12.389%	$27.333	$27.33	$27.35	$27.30
Purchase #7	$213.26	3.617%	$220.9736	$220.97	$220.95	$221.00
7 purchase totals =	$786.78		$833.3186	$833.31	$833.25	$833.30