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	$21.68	10.814%	$24.0245	$24.02	$24.00	$24.00
Purchase #2	$103.54	8.580%	$112.4237	$112.42	$112.40	$112.40
Purchase #3	$225.49	10.207%	$248.5058	$248.51	$248.50	$248.50
Purchase #4	$219.54	8.562%	$238.337	$238.34	$238.35	$238.30
Purchase #5	$88.71	13.479%	$100.6672	$100.67	$100.65	$100.70
Purchase #6	$67.72	13.821%	$77.0796	$77.08	$77.10	$77.10
Purchase #7	$169.63	5.631%	$179.1819	$179.18	$179.20	$179.20
7 purchase totals =	$896.31		$980.2197	$980.22	$980.20	$980.20