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	$6.72	13.554%	$7.6308	$7.63	$7.65	$7.60
Purchase #2	$222.31	12.397%	$249.8698	$249.87	$249.85	$249.90
Purchase #3	$44.55	3.785%	$46.2362	$46.24	$46.25	$46.20
Purchase #4	$132.89	3.441%	$137.4627	$137.46	$137.45	$137.50
Purchase #5	$218.41	9.329%	$238.7855	$238.79	$238.80	$238.80
Purchase #6	$83.40	7.339%	$89.5207	$89.52	$89.50	$89.50
Purchase #7	$124.28	4.273%	$129.5905	$129.59	$129.60	$129.60
7 purchase totals =	$832.56		$899.0962	$899.10	$899.10	$899.10