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	$9.90	5.553%	$10.4497	$10.45	$10.45	$10.40
Purchase #2	$106.88	4.742%	$111.9482	$111.95	$111.95	$111.90
Purchase #3	$69.66	3.656%	$72.2068	$72.21	$72.20	$72.20
Purchase #4	$41.55	6.429%	$44.2212	$44.22	$44.20	$44.20
Purchase #5	$204.52	6.825%	$218.4785	$218.48	$218.50	$218.50
Purchase #6	$147.27	11.661%	$164.4432	$164.44	$164.45	$164.40
Purchase #7	$29.90	9.655%	$32.7868	$32.79	$32.80	$32.80
7 purchase totals =	$609.68		$654.5344	$654.54	$654.55	$654.40