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	$73.99	6.168%	$78.5537	$78.55	$78.55	$78.60
Purchase #2	$100.43	9.328%	$109.7981	$109.80	$109.80	$109.80
Purchase #3	$56.32	10.862%	$62.4375	$62.44	$62.45	$62.40
Purchase #4	$94.48	9.454%	$103.4121	$103.41	$103.40	$103.40
Purchase #5	$178.77	7.812%	$192.7355	$192.74	$192.75	$192.70
Purchase #6	$42.81	6.245%	$45.4835	$45.48	$45.50	$45.50
Purchase #7	$235.49	9.777%	$258.5139	$258.51	$258.50	$258.50
7 purchase totals =	$782.29		$850.9343	$850.93	$850.95	$850.90