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	$82.26	10.291%	$90.7254	$90.73	$90.75	$90.70
Purchase #2	$250.54	3.297%	$258.8003	$258.80	$258.80	$258.80
Purchase #3	$165.72	8.375%	$179.5991	$179.60	$179.60	$179.60
Purchase #4	$180.58	10.192%	$198.9847	$198.98	$199.00	$199.00
Purchase #5	$122.81	12.658%	$138.3553	$138.36	$138.35	$138.40
Purchase #6	$95.53	5.296%	$100.5893	$100.59	$100.60	$100.60
Purchase #7	$55.57	12.849%	$62.7102	$62.71	$62.70	$62.70
7 purchase totals =	$953.01		$1,029.7643	$1,029.77	$1,029.80	$1,029.80