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	$228.81	12.267%	$256.8781	$256.88	$256.90	$256.90
Purchase #2	$45.55	12.640%	$51.3075	$51.31	$51.30	$51.30
Purchase #3	$178.50	11.777%	$199.5219	$199.52	$199.50	$199.50
Purchase #4	$5.89	11.495%	$6.5671	$6.57	$6.55	$6.60
Purchase #5	$71.40	13.400%	$80.9676	$80.97	$80.95	$81.00
Purchase #6	$197.62	9.525%	$216.4433	$216.44	$216.45	$216.40
Purchase #7	$50.51	10.574%	$55.8509	$55.85	$55.85	$55.90
7 purchase totals =	$778.28		$867.5364	$867.54	$867.50	$867.60