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	$145.66	13.606%	$165.4785	$165.48	$165.50	$165.50
Purchase #2	$232.50	9.331%	$254.1946	$254.19	$254.20	$254.20
Purchase #3	$137.82	5.630%	$145.5793	$145.58	$145.60	$145.60
Purchase #4	$106.64	11.499%	$118.9025	$118.90	$118.90	$118.90
Purchase #5	$25.51	7.494%	$27.4217	$27.42	$27.40	$27.40
Purchase #6	$215.68	3.384%	$222.9786	$222.98	$223.00	$223.00
Purchase #7	$73.86	12.139%	$82.8259	$82.83	$82.85	$82.80
7 purchase totals =	$937.67		$1,017.3811	$1,017.38	$1,017.45	$1,017.40