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	$40.47	13.343%	$45.8699	$45.87	$45.85	$45.90
Purchase #2	$82.31	10.318%	$90.8027	$90.80	$90.80	$90.80
Purchase #3	$81.80	9.342%	$89.4418	$89.44	$89.45	$89.40
Purchase #4	$158.60	5.629%	$167.5276	$167.53	$167.55	$167.50
Purchase #5	$239.25	3.185%	$246.8701	$246.87	$246.85	$246.90
Purchase #6	$99.35	7.210%	$106.5131	$106.51	$106.50	$106.50
Purchase #7	$205.36	6.797%	$219.3183	$219.32	$219.30	$219.30
7 purchase totals =	$907.14		$966.3435	$966.34	$966.30	$966.30