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	$25.58	7.706%	$27.5512	$27.55	$27.55	$27.60
Purchase #2	$152.39	6.453%	$162.2237	$162.22	$162.20	$162.20
Purchase #3	$151.36	10.729%	$167.5994	$167.60	$167.60	$167.60
Purchase #4	$77.84	11.793%	$87.0197	$87.02	$87.00	$87.00
Purchase #5	$97.97	6.434%	$104.2734	$104.27	$104.25	$104.30
Purchase #6	$132.89	7.271%	$142.5524	$142.55	$142.55	$142.60
Purchase #7	$54.53	13.520%	$61.9025	$61.90	$61.90	$61.90
7 purchase totals =	$692.56		$753.1223	$753.11	$753.05	$753.20