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	$241.88	7.302%	$259.5421	$259.54	$259.55	$259.50
Purchase #2	$82.50	10.163%	$90.8845	$90.88	$90.90	$90.90
Purchase #3	$157.27	4.617%	$164.5312	$164.53	$164.55	$164.50
Purchase #4	$162.66	8.385%	$176.299	$176.30	$176.30	$176.30
Purchase #5	$122.41	4.304%	$127.6785	$127.68	$127.70	$127.70
Purchase #6	$212.76	13.797%	$242.1145	$242.11	$242.10	$242.10
Purchase #7	$194.44	12.774%	$219.2778	$219.28	$219.30	$219.30
7 purchase totals =	$1,173.92		$1,280.3276	$1,280.32	$1,280.40	$1,280.30