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	$55.50	6.377%	$59.0392	$59.04	$59.05	$59.00
Purchase #2	$78.42	10.837%	$86.9184	$86.92	$86.90	$86.90
Purchase #3	$61.71	10.582%	$68.2402	$68.24	$68.25	$68.20
Purchase #4	$69.79	12.625%	$78.601	$78.60	$78.60	$78.60
Purchase #5	$99.27	9.237%	$108.4396	$108.44	$108.45	$108.40
Purchase #6	$68.79	3.114%	$70.9321	$70.93	$70.95	$70.90
Purchase #7	$201.83	3.450%	$208.7931	$208.79	$208.80	$208.80
7 purchase totals =	$635.31		$680.9636	$680.96	$681.00	$680.80