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	$122.72	10.398%	$135.4804	$135.48	$135.50	$135.50
Purchase #2	$36.78	10.175%	$40.5224	$40.52	$40.50	$40.50
Purchase #3	$148.69	13.719%	$169.0888	$169.09	$169.10	$169.10
Purchase #4	$114.42	11.621%	$127.7167	$127.72	$127.70	$127.70
Purchase #5	$103.47	5.573%	$109.2364	$109.24	$109.25	$109.20
Purchase #6	$90.36	5.804%	$95.6045	$95.60	$95.60	$95.60
Purchase #7	$122.97	3.151%	$126.8448	$126.84	$126.85	$126.80
7 purchase totals =	$739.41		$804.4940	$804.49	$804.50	$804.40