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	$16.64	7.311%	$17.8566	$17.86	$17.85	$17.90
Purchase #2	$220.75	12.495%	$248.3327	$248.33	$248.35	$248.30
Purchase #3	$150.60	6.860%	$160.9312	$160.93	$160.95	$160.90
Purchase #4	$178.88	3.757%	$185.6005	$185.60	$185.60	$185.60
Purchase #5	$165.69	5.370%	$174.5876	$174.59	$174.60	$174.60
Purchase #6	$155.39	6.272%	$165.1361	$165.14	$165.15	$165.10
Purchase #7	$46.67	13.813%	$53.1165	$53.12	$53.10	$53.10
7 purchase totals =	$934.62		$1,005.5612	$1,005.57	$1,005.60	$1,005.50