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	$75.49	9.426%	$82.6057	$82.61	$82.60	$82.60
Purchase #2	$78.85	6.464%	$83.9469	$83.95	$83.95	$83.90
Purchase #3	$163.78	7.323%	$175.7736	$175.77	$175.75	$175.80
Purchase #4	$25.77	13.392%	$29.2211	$29.22	$29.20	$29.20
Purchase #5	$38.77	6.288%	$41.2079	$41.21	$41.20	$41.20
Purchase #6	$107.34	12.359%	$120.6062	$120.61	$120.60	$120.60
Purchase #7	$100.59	12.792%	$113.4575	$113.46	$113.45	$113.50
7 purchase totals =	$590.59		$646.8189	$646.83	$646.75	$646.80