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	$100.52	6.872%	$107.4277	$107.43	$107.45	$107.40
Purchase #2	$40.63	5.589%	$42.9008	$42.90	$42.90	$42.90
Purchase #3	$245.29	8.638%	$266.4782	$266.48	$266.50	$266.50
Purchase #4	$80.60	6.487%	$85.8285	$85.83	$85.85	$85.80
Purchase #5	$32.41	3.366%	$33.5009	$33.50	$33.50	$33.50
Purchase #6	$100.85	8.738%	$109.6623	$109.66	$109.65	$109.70
Purchase #7	$154.39	12.785%	$174.1288	$174.13	$174.15	$174.10
7 purchase totals =	$754.69		$819.9272	$819.93	$820.00	$819.90