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	$28.86	9.409%	$31.5754	$31.58	$31.60	$31.60
Purchase #2	$223.82	13.318%	$253.6283	$253.63	$253.65	$253.60
Purchase #3	$245.53	13.591%	$278.9	$278.90	$278.90	$278.90
Purchase #4	$99.97	7.729%	$107.6967	$107.70	$107.70	$107.70
Purchase #5	$162.79	5.746%	$172.1439	$172.14	$172.15	$172.10
Purchase #6	$197.35	4.177%	$205.5933	$205.59	$205.60	$205.60
Purchase #7	$247.50	4.601%	$258.8875	$258.89	$258.90	$258.90
7 purchase totals =	$1,205.82		$1,308.4251	$1,308.43	$1,308.50	$1,308.40