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	$138.53	5.735%	$146.4747	$146.47	$146.45	$146.50
Purchase #2	$110.44	12.675%	$124.4383	$124.44	$124.45	$124.40
Purchase #3	$23.27	5.428%	$24.5331	$24.53	$24.55	$24.50
Purchase #4	$115.52	6.700%	$123.2598	$123.26	$123.25	$123.30
Purchase #5	$35.54	4.677%	$37.2022	$37.20	$37.20	$37.20
Purchase #6	$18.99	10.710%	$21.0238	$21.02	$21.00	$21.00
Purchase #7	$166.98	7.709%	$179.8525	$179.85	$179.85	$179.90
7 purchase totals =	$609.27		$656.7844	$656.77	$656.75	$656.80