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	$21.30	7.445%	$22.8858	$22.89	$22.90	$22.90
Purchase #2	$217.52	9.419%	$238.0082	$238.01	$238.00	$238.00
Purchase #3	$175.78	8.180%	$190.1588	$190.16	$190.15	$190.20
Purchase #4	$181.71	4.810%	$190.4503	$190.45	$190.45	$190.50
Purchase #5	$19.69	11.285%	$21.912	$21.91	$21.90	$21.90
Purchase #6	$79.75	13.239%	$90.3081	$90.31	$90.30	$90.30
Purchase #7	$16.59	11.782%	$18.5446	$18.54	$18.55	$18.50
7 purchase totals =	$712.34		$772.2678	$772.27	$772.25	$772.30