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	$162.92	6.462%	$173.4479	$173.45	$173.45	$173.40
Purchase #2	$137.69	9.250%	$150.4263	$150.43	$150.45	$150.40
Purchase #3	$239.55	6.382%	$254.8381	$254.84	$254.85	$254.80
Purchase #4	$131.87	4.193%	$137.3993	$137.40	$137.40	$137.40
Purchase #5	$80.91	11.462%	$90.1839	$90.18	$90.20	$90.20
Purchase #6	$16.74	7.585%	$18.0097	$18.01	$18.00	$18.00
Purchase #7	$49.75	13.654%	$56.5429	$56.54	$56.55	$56.50
7 purchase totals =	$819.43		$880.8481	$880.85	$880.90	$880.70