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	$105.71	9.600%	$115.8582	$115.86	$115.85	$115.90
Purchase #2	$127.63	10.780%	$141.3885	$141.39	$141.40	$141.40
Purchase #3	$136.98	11.435%	$152.6437	$152.64	$152.65	$152.60
Purchase #4	$51.25	11.529%	$57.1586	$57.16	$57.15	$57.20
Purchase #5	$56.43	8.490%	$61.2209	$61.22	$61.20	$61.20
Purchase #6	$111.32	11.617%	$124.252	$124.25	$124.25	$124.30
Purchase #7	$204.27	6.772%	$218.1032	$218.10	$218.10	$218.10
7 purchase totals =	$793.59		$870.6251	$870.62	$870.60	$870.70