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	$123.49	7.282%	$132.4825	$132.48	$132.50	$132.50
Purchase #2	$200.27	6.118%	$212.5225	$212.52	$212.50	$212.50
Purchase #3	$242.56	5.227%	$255.2386	$255.24	$255.25	$255.20
Purchase #4	$85.64	4.233%	$89.2651	$89.27	$89.25	$89.30
Purchase #5	$137.74	5.488%	$145.2992	$145.30	$145.30	$145.30
Purchase #6	$24.82	10.603%	$27.4517	$27.45	$27.45	$27.50
Purchase #7	$75.73	10.534%	$83.7074	$83.71	$83.70	$83.70
7 purchase totals =	$890.25		$945.9670	$945.97	$945.95	$946.00