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	$30.35	7.275%	$32.558	$32.56	$32.55	$32.60
Purchase #2	$250.83	6.414%	$266.9182	$266.92	$266.90	$266.90
Purchase #3	$146.80	6.439%	$156.2525	$156.25	$156.25	$156.30
Purchase #4	$54.68	9.556%	$59.9052	$59.91	$59.90	$59.90
Purchase #5	$109.82	9.576%	$120.3364	$120.34	$120.35	$120.30
Purchase #6	$204.55	10.576%	$226.1832	$226.18	$226.20	$226.20
Purchase #7	$128.40	7.133%	$137.5588	$137.56	$137.55	$137.60
7 purchase totals =	$925.43		$999.7123	$999.72	$999.70	$999.80