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	$242.34	6.395%	$257.8376	$257.84	$257.85	$257.80
Purchase #2	$64.81	3.760%	$67.2469	$67.25	$67.25	$67.20
Purchase #3	$203.75	9.314%	$222.7273	$222.73	$222.75	$222.70
Purchase #4	$51.80	5.605%	$54.7034	$54.70	$54.70	$54.70
Purchase #5	$82.29	5.504%	$86.8192	$86.82	$86.80	$86.80
Purchase #6	$105.47	7.574%	$113.4583	$113.46	$113.45	$113.50
Purchase #7	$86.36	9.218%	$94.3207	$94.32	$94.30	$94.30
7 purchase totals =	$836.82		$897.1134	$897.12	$897.10	$897.00