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	$29.27	12.236%	$32.8515	$32.85	$32.85	$32.90
Purchase #2	$127.31	9.790%	$139.7736	$139.77	$139.75	$139.80
Purchase #3	$168.49	10.521%	$186.2168	$186.22	$186.20	$186.20
Purchase #4	$215.56	3.774%	$223.6952	$223.70	$223.70	$223.70
Purchase #5	$21.90	11.380%	$24.3922	$24.39	$24.40	$24.40
Purchase #6	$125.81	4.118%	$130.9909	$130.99	$131.00	$131.00
Purchase #7	$158.60	6.482%	$168.8805	$168.88	$168.90	$168.90
7 purchase totals =	$846.94		$906.8007	$906.80	$906.80	$906.90