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	$80.40	4.443%	$83.9722	$83.97	$83.95	$84.00
Purchase #2	$94.59	13.624%	$107.4769	$107.48	$107.50	$107.50
Purchase #3	$92.73	12.668%	$104.477	$104.48	$104.50	$104.50
Purchase #4	$42.86	4.761%	$44.9006	$44.90	$44.90	$44.90
Purchase #5	$149.98	4.233%	$156.3287	$156.33	$156.35	$156.30
Purchase #6	$78.92	12.176%	$88.5293	$88.53	$88.55	$88.50
Purchase #7	$131.29	10.103%	$144.5542	$144.55	$144.55	$144.60
7 purchase totals =	$670.77		$730.2389	$730.24	$730.30	$730.30