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	$50.88	5.812%	$53.8371	$53.84	$53.85	$53.80
Purchase #2	$85.38	5.421%	$90.0084	$90.01	$90.00	$90.00
Purchase #3	$167.61	8.170%	$181.3037	$181.30	$181.30	$181.30
Purchase #4	$160.69	6.672%	$171.4112	$171.41	$171.40	$171.40
Purchase #5	$38.79	7.262%	$41.6069	$41.61	$41.60	$41.60
Purchase #6	$63.41	11.347%	$70.6051	$70.61	$70.60	$70.60
Purchase #7	$45.38	9.703%	$49.7832	$49.78	$49.80	$49.80
7 purchase totals =	$612.14		$658.5556	$658.56	$658.55	$658.50