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	$36.41	4.800%	$38.1577	$38.16	$38.15	$38.20
Purchase #2	$55.86	12.436%	$62.8067	$62.81	$62.80	$62.80
Purchase #3	$91.66	13.708%	$104.2248	$104.22	$104.20	$104.20
Purchase #4	$96.84	3.546%	$100.2739	$100.27	$100.25	$100.30
Purchase #5	$122.96	9.577%	$134.7359	$134.74	$134.75	$134.70
Purchase #6	$121.56	6.848%	$129.8844	$129.88	$129.90	$129.90
Purchase #7	$61.25	13.406%	$69.4612	$69.46	$69.45	$69.50
7 purchase totals =	$586.54		$639.5446	$639.54	$639.50	$639.60