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	$35.82	7.393%	$38.4682	$38.47	$38.45	$38.50
Purchase #2	$142.45	7.656%	$153.356	$153.36	$153.35	$153.40
Purchase #3	$138.54	4.269%	$144.4543	$144.45	$144.45	$144.50
Purchase #4	$187.68	10.689%	$207.7411	$207.74	$207.75	$207.70
Purchase #5	$158.69	6.277%	$168.651	$168.65	$168.65	$168.70
Purchase #6	$133.52	6.474%	$142.1641	$142.16	$142.15	$142.20
Purchase #7	$173.89	12.801%	$196.1497	$196.15	$196.15	$196.10
7 purchase totals =	$970.59		$1,050.9844	$1,050.98	$1,050.95	$1,051.10