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	$61.62	13.257%	$69.789	$69.79	$69.80	$69.80
Purchase #2	$26.45	9.453%	$28.9503	$28.95	$28.95	$29.00
Purchase #3	$172.78	8.488%	$187.4456	$187.45	$187.45	$187.40
Purchase #4	$174.35	12.689%	$196.4733	$196.47	$196.45	$196.50
Purchase #5	$45.85	5.349%	$48.3025	$48.30	$48.30	$48.30
Purchase #6	$133.72	4.534%	$139.7829	$139.78	$139.80	$139.80
Purchase #7	$140.53	10.373%	$155.1072	$155.11	$155.10	$155.10
7 purchase totals =	$755.30		$825.8508	$825.85	$825.85	$825.90