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	$18.98	12.179%	$21.2916	$21.29	$21.30	$21.30
Purchase #2	$100.62	5.854%	$106.5103	$106.51	$106.50	$106.50
Purchase #3	$222.78	9.587%	$244.1379	$244.14	$244.15	$244.10
Purchase #4	$76.89	5.372%	$81.0205	$81.02	$81.00	$81.00
Purchase #5	$50.38	6.705%	$53.758	$53.76	$53.75	$53.80
Purchase #6	$154.83	12.278%	$173.84	$173.84	$173.85	$173.80
Purchase #7	$142.43	5.372%	$150.0813	$150.08	$150.10	$150.10
7 purchase totals =	$766.91		$830.6396	$830.64	$830.65	$830.60