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	$6.85	13.864%	$7.7997	$7.80	$7.80	$7.80
Purchase #2	$93.50	13.289%	$105.9252	$105.93	$105.95	$105.90
Purchase #3	$182.28	3.571%	$188.7892	$188.79	$188.80	$188.80
Purchase #4	$48.28	6.815%	$51.5703	$51.57	$51.55	$51.60
Purchase #5	$5.94	13.490%	$6.7413	$6.74	$6.75	$6.70
Purchase #6	$54.79	8.350%	$59.365	$59.37	$59.35	$59.40
Purchase #7	$164.92	13.445%	$187.0935	$187.09	$187.10	$187.10
7 purchase totals =	$556.56		$607.2842	$607.29	$607.30	$607.30