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	$38.84	10.291%	$42.837	$42.84	$42.85	$42.80
Purchase #2	$166.74	13.679%	$189.5484	$189.55	$189.55	$189.50
Purchase #3	$201.85	5.425%	$212.8004	$212.80	$212.80	$212.80
Purchase #4	$71.38	8.426%	$77.3945	$77.39	$77.40	$77.40
Purchase #5	$77.59	10.696%	$85.889	$85.89	$85.90	$85.90
Purchase #6	$62.56	13.380%	$70.9305	$70.93	$70.95	$70.90
Purchase #7	$167.83	11.520%	$187.164	$187.16	$187.15	$187.20
7 purchase totals =	$786.79		$866.5638	$866.56	$866.60	$866.50