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	$56.69	6.770%	$60.5279	$60.53	$60.55	$60.50
Purchase #2	$135.83	12.283%	$152.514	$152.51	$152.50	$152.50
Purchase #3	$200.59	8.604%	$217.8488	$217.85	$217.85	$217.80
Purchase #4	$182.60	7.404%	$196.1197	$196.12	$196.10	$196.10
Purchase #5	$217.71	3.546%	$225.43	$225.43	$225.45	$225.40
Purchase #6	$207.82	12.379%	$233.546	$233.55	$233.55	$233.50
Purchase #7	$242.44	7.631%	$260.9406	$260.94	$260.95	$260.90
7 purchase totals =	$1,243.68		$1,346.9270	$1,346.93	$1,346.95	$1,346.70