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	$248.53	4.767%	$260.3774	$260.38	$260.40	$260.40
Purchase #2	$75.78	6.653%	$80.8216	$80.82	$80.80	$80.80
Purchase #3	$109.57	10.557%	$121.1373	$121.14	$121.15	$121.10
Purchase #4	$178.57	10.223%	$196.8252	$196.83	$196.85	$196.80
Purchase #5	$183.53	11.665%	$204.9388	$204.94	$204.95	$204.90
Purchase #6	$15.33	13.655%	$17.4233	$17.42	$17.40	$17.40
Purchase #7	$84.82	6.683%	$90.4885	$90.49	$90.50	$90.50
7 purchase totals =	$896.13		$972.0121	$972.02	$972.05	$971.90