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	$32.55	3.510%	$33.6925	$33.69	$33.70	$33.70
Purchase #2	$45.58	10.681%	$50.4484	$50.45	$50.45	$50.40
Purchase #3	$65.63	9.714%	$72.0053	$72.01	$72.00	$72.00
Purchase #4	$129.47	13.807%	$147.3459	$147.35	$147.35	$147.30
Purchase #5	$120.51	10.366%	$133.0021	$133.00	$133.00	$133.00
Purchase #6	$165.98	4.497%	$173.4441	$173.44	$173.45	$173.40
Purchase #7	$208.88	13.275%	$236.6088	$236.61	$236.60	$236.60
7 purchase totals =	$768.60		$846.5471	$846.55	$846.55	$846.40