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	$53.42	4.106%	$55.6134	$55.61	$55.60	$55.60
Purchase #2	$78.92	9.353%	$86.3014	$86.30	$86.30	$86.30
Purchase #3	$177.42	7.611%	$190.9234	$190.92	$190.90	$190.90
Purchase #4	$101.73	4.755%	$106.5673	$106.57	$106.55	$106.60
Purchase #5	$123.98	12.788%	$139.8346	$139.83	$139.85	$139.80
Purchase #6	$64.63	11.609%	$72.1329	$72.13	$72.15	$72.10
Purchase #7	$202.97	5.576%	$214.2876	$214.29	$214.30	$214.30
7 purchase totals =	$803.07		$865.6606	$865.65	$865.65	$865.60