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	$99.49	3.537%	$103.009	$103.01	$103.00	$103.00
Purchase #2	$97.83	11.818%	$109.3915	$109.39	$109.40	$109.40
Purchase #3	$228.65	12.163%	$256.4607	$256.46	$256.45	$256.50
Purchase #4	$6.67	10.789%	$7.3896	$7.39	$7.40	$7.40
Purchase #5	$121.33	10.412%	$133.9629	$133.96	$133.95	$134.00
Purchase #6	$206.42	6.225%	$219.2696	$219.27	$219.25	$219.30
Purchase #7	$15.77	10.419%	$17.4131	$17.41	$17.40	$17.40
7 purchase totals =	$776.16		$846.8964	$846.89	$846.85	$847.00