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	$153.92	11.446%	$171.5377	$171.54	$171.55	$171.50
Purchase #2	$131.54	5.692%	$139.0273	$139.03	$139.05	$139.00
Purchase #3	$67.71	13.330%	$76.7357	$76.74	$76.75	$76.70
Purchase #4	$78.57	12.482%	$88.3771	$88.38	$88.40	$88.40
Purchase #5	$179.83	9.312%	$196.5758	$196.58	$196.60	$196.60
Purchase #6	$116.44	9.116%	$127.0547	$127.05	$127.05	$127.10
Purchase #7	$168.79	11.182%	$187.6641	$187.66	$187.65	$187.70
7 purchase totals =	$896.80		$986.9724	$986.98	$987.05	$987.00