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	$22.34	8.148%	$24.1603	$24.16	$24.15	$24.20
Purchase #2	$53.72	12.466%	$60.4167	$60.42	$60.40	$60.40
Purchase #3	$59.46	12.804%	$67.0733	$67.07	$67.05	$67.10
Purchase #4	$112.65	5.684%	$119.053	$119.05	$119.05	$119.10
Purchase #5	$190.58	7.417%	$204.7153	$204.72	$204.70	$204.70
Purchase #6	$236.77	12.269%	$265.8193	$265.82	$265.80	$265.80
Purchase #7	$89.72	12.413%	$100.8569	$100.86	$100.85	$100.90
7 purchase totals =	$765.24		$842.0948	$842.10	$842.00	$842.20