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	$35.34	11.276%	$39.3249	$39.32	$39.30	$39.30
Purchase #2	$55.85	10.463%	$61.6936	$61.69	$61.70	$61.70
Purchase #3	$78.40	10.404%	$86.5567	$86.56	$86.55	$86.60
Purchase #4	$219.68	8.633%	$238.645	$238.65	$238.65	$238.60
Purchase #5	$212.44	4.617%	$222.2484	$222.25	$222.25	$222.20
Purchase #6	$23.86	12.748%	$26.9017	$26.90	$26.90	$26.90
Purchase #7	$54.66	4.498%	$57.1186	$57.12	$57.10	$57.10
7 purchase totals =	$680.23		$732.4889	$732.49	$732.45	$732.40