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	$136.60	11.804%	$152.7243	$152.72	$152.70	$152.70
Purchase #2	$205.47	5.575%	$216.925	$216.93	$216.95	$216.90
Purchase #3	$113.41	8.577%	$123.1372	$123.14	$123.15	$123.10
Purchase #4	$86.32	10.765%	$95.6123	$95.61	$95.60	$95.60
Purchase #5	$227.42	12.214%	$255.1971	$255.20	$255.20	$255.20
Purchase #6	$27.80	3.225%	$28.6966	$28.70	$28.70	$28.70
Purchase #7	$30.98	8.238%	$33.5321	$33.53	$33.55	$33.50
7 purchase totals =	$828.00		$905.8246	$905.83	$905.85	$905.70