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	$78.97	13.351%	$89.5133	$89.51	$89.50	$89.50
Purchase #2	$128.55	12.325%	$144.3938	$144.39	$144.40	$144.40
Purchase #3	$109.90	7.536%	$118.1821	$118.18	$118.20	$118.20
Purchase #4	$187.73	7.567%	$201.9355	$201.94	$201.95	$201.90
Purchase #5	$137.73	9.581%	$150.9259	$150.93	$150.95	$150.90
Purchase #6	$221.80	12.475%	$249.4696	$249.47	$249.45	$249.50
Purchase #7	$116.74	11.385%	$130.0308	$130.03	$130.05	$130.00
7 purchase totals =	$981.42		$1,084.4510	$1,084.45	$1,084.50	$1,084.40