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	$100.56	10.400%	$111.0182	$111.02	$111.00	$111.00
Purchase #2	$54.86	8.556%	$59.5538	$59.55	$59.55	$59.60
Purchase #3	$200.63	10.362%	$221.4193	$221.42	$221.40	$221.40
Purchase #4	$113.55	6.530%	$120.9648	$120.96	$120.95	$121.00
Purchase #5	$31.68	5.640%	$33.4668	$33.47	$33.45	$33.50
Purchase #6	$59.98	10.724%	$66.4123	$66.41	$66.40	$66.40
Purchase #7	$182.67	8.563%	$198.312	$198.31	$198.30	$198.30
7 purchase totals =	$743.93		$811.1472	$811.14	$811.05	$811.20