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	$45.96	10.567%	$50.8166	$50.82	$50.80	$50.80
Purchase #2	$167.42	10.250%	$184.5806	$184.58	$184.60	$184.60
Purchase #3	$221.33	8.684%	$240.5503	$240.55	$240.55	$240.60
Purchase #4	$66.32	7.689%	$71.4193	$71.42	$71.40	$71.40
Purchase #5	$109.72	11.172%	$121.9779	$121.98	$122.00	$122.00
Purchase #6	$200.76	8.856%	$218.5393	$218.54	$218.55	$218.50
Purchase #7	$117.43	5.410%	$123.783	$123.78	$123.80	$123.80
7 purchase totals =	$928.94		$1,011.6670	$1,011.67	$1,011.70	$1,011.70