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	$48.27	13.588%	$54.8289	$54.83	$54.85	$54.80
Purchase #2	$213.89	13.800%	$243.4068	$243.41	$243.40	$243.40
Purchase #3	$193.56	8.525%	$210.061	$210.06	$210.05	$210.10
Purchase #4	$72.86	11.126%	$80.9664	$80.97	$80.95	$81.00
Purchase #5	$137.27	4.451%	$143.3799	$143.38	$143.40	$143.40
Purchase #6	$28.94	8.657%	$31.4453	$31.45	$31.45	$31.40
Purchase #7	$129.26	10.219%	$142.4691	$142.47	$142.45	$142.50
7 purchase totals =	$824.05		$906.5574	$906.57	$906.55	$906.60