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	$52.43	5.484%	$55.3053	$55.31	$55.30	$55.30
Purchase #2	$78.98	4.303%	$82.3785	$82.38	$82.40	$82.40
Purchase #3	$101.32	6.590%	$107.997	$108.00	$108.00	$108.00
Purchase #4	$77.71	5.572%	$82.04	$82.04	$82.05	$82.00
Purchase #5	$135.80	9.355%	$148.5041	$148.50	$148.50	$148.50
Purchase #6	$47.56	12.625%	$53.5645	$53.56	$53.55	$53.60
Purchase #7	$55.99	8.261%	$60.6153	$60.62	$60.60	$60.60
7 purchase totals =	$549.79		$590.4047	$590.41	$590.40	$590.40