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	$81.33	11.217%	$90.4528	$90.45	$90.45	$90.50
Purchase #2	$151.36	11.218%	$168.3396	$168.34	$168.35	$168.30
Purchase #3	$101.64	4.161%	$105.8692	$105.87	$105.85	$105.90
Purchase #4	$71.38	11.513%	$79.598	$79.60	$79.60	$79.60
Purchase #5	$22.51	4.656%	$23.5581	$23.56	$23.55	$23.60
Purchase #6	$6.72	9.806%	$7.379	$7.38	$7.40	$7.40
Purchase #7	$109.65	12.196%	$123.0229	$123.02	$123.00	$123.00
7 purchase totals =	$544.59		$598.2196	$598.22	$598.20	$598.30