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	$112.59	3.272%	$116.2739	$116.27	$116.25	$116.30
Purchase #2	$122.73	10.635%	$135.7823	$135.78	$135.80	$135.80
Purchase #3	$233.37	3.145%	$240.7095	$240.71	$240.70	$240.70
Purchase #4	$85.77	4.808%	$89.8938	$89.89	$89.90	$89.90
Purchase #5	$74.97	9.584%	$82.1551	$82.16	$82.15	$82.20
Purchase #6	$96.86	12.556%	$109.0217	$109.02	$109.00	$109.00
Purchase #7	$45.94	5.674%	$48.5466	$48.55	$48.55	$48.50
7 purchase totals =	$772.23		$822.3829	$822.38	$822.35	$822.40