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	$42.90	11.520%	$47.8421	$47.84	$47.85	$47.80
Purchase #2	$240.96	6.124%	$255.7164	$255.72	$255.70	$255.70
Purchase #3	$130.80	11.455%	$145.7831	$145.78	$145.80	$145.80
Purchase #4	$90.51	9.209%	$98.8451	$98.85	$98.85	$98.80
Purchase #5	$52.34	4.703%	$54.8016	$54.80	$54.80	$54.80
Purchase #6	$60.53	8.645%	$65.7628	$65.76	$65.75	$65.80
Purchase #7	$133.89	13.692%	$152.2222	$152.22	$152.20	$152.20
7 purchase totals =	$751.93		$820.9733	$820.97	$820.95	$820.90