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	$38.98	9.624%	$42.7314	$42.73	$42.75	$42.70
Purchase #2	$217.82	13.210%	$246.594	$246.59	$246.60	$246.60
Purchase #3	$162.74	7.555%	$175.035	$175.04	$175.05	$175.00
Purchase #4	$134.83	8.695%	$146.5535	$146.55	$146.55	$146.60
Purchase #5	$44.82	11.698%	$50.063	$50.06	$50.05	$50.10
Purchase #6	$100.75	4.526%	$105.3099	$105.31	$105.30	$105.30
Purchase #7	$205.48	4.789%	$215.3204	$215.32	$215.30	$215.30
7 purchase totals =	$905.42		$981.6072	$981.60	$981.60	$981.60