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	$90.74	13.508%	$102.9972	$103.00	$103.00	$103.00
Purchase #2	$85.98	9.182%	$93.8747	$93.87	$93.85	$93.90
Purchase #3	$127.74	10.642%	$141.3341	$141.33	$141.35	$141.30
Purchase #4	$236.36	7.278%	$253.5623	$253.56	$253.55	$253.60
Purchase #5	$230.82	13.193%	$261.2721	$261.27	$261.25	$261.30
Purchase #6	$55.43	10.132%	$61.0462	$61.05	$61.05	$61.00
Purchase #7	$83.76	8.403%	$90.7984	$90.80	$90.80	$90.80
7 purchase totals =	$910.83		$1,004.8850	$1,004.88	$1,004.85	$1,004.90