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	$75.88	3.494%	$78.5312	$78.53	$78.55	$78.50
Purchase #2	$171.70	9.737%	$188.4184	$188.42	$188.40	$188.40
Purchase #3	$13.57	10.646%	$15.0147	$15.01	$15.00	$15.00
Purchase #4	$35.68	8.426%	$38.6864	$38.69	$38.70	$38.70
Purchase #5	$32.44	4.469%	$33.8897	$33.89	$33.90	$33.90
Purchase #6	$42.31	13.779%	$48.1399	$48.14	$48.15	$48.10
Purchase #7	$245.76	5.567%	$259.4415	$259.44	$259.45	$259.40
7 purchase totals =	$617.34		$662.1218	$662.12	$662.15	$662.00