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	$170.83	5.224%	$179.7542	$179.75	$179.75	$179.80
Purchase #2	$244.27	12.457%	$274.6987	$274.70	$274.70	$274.70
Purchase #3	$33.86	13.589%	$38.4612	$38.46	$38.45	$38.50
Purchase #4	$224.78	11.453%	$250.5241	$250.52	$250.50	$250.50
Purchase #5	$141.97	7.605%	$152.7668	$152.77	$152.75	$152.80
Purchase #6	$116.58	13.128%	$131.8846	$131.88	$131.90	$131.90
Purchase #7	$27.31	5.642%	$28.8508	$28.85	$28.85	$28.90
7 purchase totals =	$959.60		$1,056.9404	$1,056.93	$1,056.90	$1,057.10