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	$107.83	3.299%	$111.3873	$111.39	$111.40	$111.40
Purchase #2	$211.98	12.397%	$238.2592	$238.26	$238.25	$238.30
Purchase #3	$77.64	11.107%	$86.2635	$86.26	$86.25	$86.30
Purchase #4	$167.82	11.334%	$186.8407	$186.84	$186.85	$186.80
Purchase #5	$203.83	11.674%	$227.6251	$227.63	$227.65	$227.60
Purchase #6	$222.75	12.475%	$250.5381	$250.54	$250.55	$250.50
Purchase #7	$248.25	13.636%	$282.1014	$282.10	$282.10	$282.10
7 purchase totals =	$1,240.10		$1,383.0153	$1,383.02	$1,383.05	$1,383.00