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	$15.69	6.280%	$16.6753	$16.68	$16.70	$16.70
Purchase #2	$237.36	3.453%	$245.556	$245.56	$245.55	$245.60
Purchase #3	$214.85	11.774%	$240.1464	$240.15	$240.15	$240.10
Purchase #4	$62.88	13.149%	$71.1481	$71.15	$71.15	$71.10
Purchase #5	$99.49	12.553%	$111.979	$111.98	$112.00	$112.00
Purchase #6	$49.57	13.287%	$56.1564	$56.16	$56.15	$56.20
Purchase #7	$236.32	10.794%	$261.8284	$261.83	$261.85	$261.80
7 purchase totals =	$916.16		$1,003.4896	$1,003.51	$1,003.55	$1,003.50