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	$78.73	7.406%	$84.5607	$84.56	$84.55	$84.60
Purchase #2	$134.97	5.660%	$142.6093	$142.61	$142.60	$142.60
Purchase #3	$118.97	12.471%	$133.8067	$133.81	$133.80	$133.80
Purchase #4	$44.42	3.518%	$45.9827	$45.98	$46.00	$46.00
Purchase #5	$18.81	11.530%	$20.9788	$20.98	$21.00	$21.00
Purchase #6	$179.54	9.553%	$196.6915	$196.69	$196.70	$196.70
Purchase #7	$250.88	13.690%	$285.2255	$285.23	$285.25	$285.20
7 purchase totals =	$826.32		$909.8552	$909.86	$909.90	$909.90