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	$37.57	12.480%	$42.2587	$42.26	$42.25	$42.30
Purchase #2	$81.55	10.840%	$90.39	$90.39	$90.40	$90.40
Purchase #3	$179.74	5.184%	$189.0577	$189.06	$189.05	$189.10
Purchase #4	$191.34	8.195%	$207.0203	$207.02	$207.00	$207.00
Purchase #5	$132.75	8.834%	$144.4771	$144.48	$144.50	$144.50
Purchase #6	$222.85	8.639%	$242.102	$242.10	$242.10	$242.10
Purchase #7	$132.57	5.246%	$139.5246	$139.52	$139.50	$139.50
7 purchase totals =	$978.37		$1,054.8304	$1,054.83	$1,054.80	$1,054.90