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	$30.56	7.571%	$32.8737	$32.87	$32.85	$32.90
Purchase #2	$23.87	6.580%	$25.4406	$25.44	$25.45	$25.40
Purchase #3	$45.62	13.426%	$51.7449	$51.74	$51.75	$51.70
Purchase #4	$17.53	4.603%	$18.3369	$18.34	$18.35	$18.30
Purchase #5	$128.58	11.127%	$142.8871	$142.89	$142.90	$142.90
Purchase #6	$241.56	8.560%	$262.2375	$262.24	$262.25	$262.20
Purchase #7	$36.94	12.345%	$41.5002	$41.50	$41.50	$41.50
7 purchase totals =	$524.66		$575.0209	$575.02	$575.05	$574.90