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	$54.47	6.328%	$57.9169	$57.92	$57.90	$57.90
Purchase #2	$70.96	8.828%	$77.2243	$77.22	$77.20	$77.20
Purchase #3	$37.68	11.575%	$42.0415	$42.04	$42.05	$42.00
Purchase #4	$243.81	4.725%	$255.33	$255.33	$255.35	$255.30
Purchase #5	$93.73	6.789%	$100.0933	$100.09	$100.10	$100.10
Purchase #6	$79.32	6.190%	$84.2299	$84.23	$84.25	$84.20
Purchase #7	$84.30	13.645%	$95.8027	$95.80	$95.80	$95.80
7 purchase totals =	$664.27		$712.6386	$712.63	$712.65	$712.50