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	$147.96	13.817%	$168.4036	$168.40	$168.40	$168.40
Purchase #2	$74.59	10.812%	$82.6547	$82.65	$82.65	$82.70
Purchase #3	$163.57	13.447%	$185.5653	$185.57	$185.55	$185.60
Purchase #4	$93.31	7.210%	$100.0377	$100.04	$100.05	$100.00
Purchase #5	$176.99	7.141%	$189.6289	$189.63	$189.65	$189.60
Purchase #6	$44.93	11.160%	$49.9442	$49.94	$49.95	$49.90
Purchase #7	$96.59	4.454%	$100.8921	$100.89	$100.90	$100.90
7 purchase totals =	$797.94		$877.1265	$877.12	$877.15	$877.10