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	$89.38	10.116%	$98.4217	$98.42	$98.40	$98.40
Purchase #2	$183.73	9.748%	$201.64	$201.64	$201.65	$201.60
Purchase #3	$107.33	5.176%	$112.8854	$112.89	$112.90	$112.90
Purchase #4	$193.66	6.295%	$205.8509	$205.85	$205.85	$205.90
Purchase #5	$76.90	8.336%	$83.3104	$83.31	$83.30	$83.30
Purchase #6	$227.25	7.604%	$244.5301	$244.53	$244.55	$244.50
Purchase #7	$95.35	4.343%	$99.4911	$99.49	$99.50	$99.50
7 purchase totals =	$973.60		$1,046.1296	$1,046.13	$1,046.15	$1,046.10