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	$120.74	9.272%	$131.935	$131.94	$131.95	$131.90
Purchase #2	$181.61	3.286%	$187.5777	$187.58	$187.60	$187.60
Purchase #3	$16.64	11.727%	$18.5914	$18.59	$18.60	$18.60
Purchase #4	$165.47	4.316%	$172.6117	$172.61	$172.60	$172.60
Purchase #5	$183.41	8.461%	$198.9283	$198.93	$198.95	$198.90
Purchase #6	$165.79	12.454%	$186.4375	$186.44	$186.45	$186.40
Purchase #7	$175.64	8.634%	$190.8048	$190.80	$190.80	$190.80
7 purchase totals =	$1,009.30		$1,086.8864	$1,086.89	$1,086.95	$1,086.80