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	$101.47	8.199%	$109.7895	$109.79	$109.80	$109.80
Purchase #2	$6.65	11.261%	$7.3989	$7.40	$7.40	$7.40
Purchase #3	$225.61	10.428%	$249.1366	$249.14	$249.15	$249.10
Purchase #4	$40.83	11.254%	$45.425	$45.43	$45.45	$45.40
Purchase #5	$117.72	13.167%	$133.2202	$133.22	$133.20	$133.20
Purchase #6	$43.99	4.858%	$46.127	$46.13	$46.15	$46.10
Purchase #7	$36.98	12.335%	$41.5415	$41.54	$41.55	$41.50
7 purchase totals =	$573.25		$632.6387	$632.65	$632.70	$632.50