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	$30.58	11.497%	$34.0958	$34.10	$34.10	$34.10
Purchase #2	$121.68	4.760%	$127.472	$127.47	$127.45	$127.50
Purchase #3	$119.82	12.465%	$134.7556	$134.76	$134.75	$134.80
Purchase #4	$188.31	4.313%	$196.4318	$196.43	$196.45	$196.40
Purchase #5	$224.55	12.736%	$253.1487	$253.15	$253.15	$253.10
Purchase #6	$16.65	12.715%	$18.767	$18.77	$18.75	$18.80
Purchase #7	$37.79	8.843%	$41.1318	$41.13	$41.15	$41.10
7 purchase totals =	$739.38		$805.8027	$805.81	$805.80	$805.80