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	$200.70	12.795%	$226.3796	$226.38	$226.40	$226.40
Purchase #2	$62.34	7.607%	$67.0822	$67.08	$67.10	$67.10
Purchase #3	$183.60	8.678%	$199.5328	$199.53	$199.55	$199.50
Purchase #4	$219.47	10.157%	$241.7616	$241.76	$241.75	$241.80
Purchase #5	$168.38	8.825%	$183.2395	$183.24	$183.25	$183.20
Purchase #6	$117.76	11.589%	$131.4072	$131.41	$131.40	$131.40
Purchase #7	$36.77	11.160%	$40.8735	$40.87	$40.85	$40.90
7 purchase totals =	$989.02		$1,090.2764	$1,090.27	$1,090.30	$1,090.30