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	$59.43	13.442%	$67.4186	$67.42	$67.40	$67.40
Purchase #2	$108.59	5.538%	$114.6037	$114.60	$114.60	$114.60
Purchase #3	$25.69	13.846%	$29.247	$29.25	$29.25	$29.20
Purchase #4	$163.54	6.842%	$174.7294	$174.73	$174.75	$174.70
Purchase #5	$72.85	13.208%	$82.472	$82.47	$82.45	$82.50
Purchase #6	$101.92	5.824%	$107.8558	$107.86	$107.85	$107.90
Purchase #7	$235.25	4.193%	$245.114	$245.11	$245.10	$245.10
7 purchase totals =	$767.27		$821.4405	$821.44	$821.40	$821.40