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	$74.70	7.112%	$80.0127	$80.01	$80.00	$80.00
Purchase #2	$98.30	13.532%	$111.602	$111.60	$111.60	$111.60
Purchase #3	$178.30	6.297%	$189.5276	$189.53	$189.55	$189.50
Purchase #4	$86.70	10.789%	$96.0541	$96.05	$96.05	$96.10
Purchase #5	$180.48	3.115%	$186.102	$186.10	$186.10	$186.10
Purchase #6	$230.80	13.683%	$262.3804	$262.38	$262.40	$262.40
Purchase #7	$156.60	5.226%	$164.7839	$164.78	$164.80	$164.80
7 purchase totals =	$1,005.88		$1,090.4627	$1,090.45	$1,090.50	$1,090.50