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	$51.98	4.488%	$54.3129	$54.31	$54.30	$54.30
Purchase #2	$139.64	3.122%	$143.9996	$144.00	$144.00	$144.00
Purchase #3	$243.95	9.184%	$266.3544	$266.35	$266.35	$266.40
Purchase #4	$38.54	9.766%	$42.3038	$42.30	$42.30	$42.30
Purchase #5	$173.94	12.791%	$196.1887	$196.19	$196.20	$196.20
Purchase #6	$164.70	13.739%	$187.3281	$187.33	$187.35	$187.30
Purchase #7	$240.53	10.561%	$265.9324	$265.93	$265.95	$265.90
7 purchase totals =	$1,053.28		$1,156.4199	$1,156.41	$1,156.45	$1,156.40