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	$183.53	4.336%	$191.4879	$191.49	$191.50	$191.50
Purchase #2	$240.87	9.818%	$264.5186	$264.52	$264.50	$264.50
Purchase #3	$191.61	13.870%	$218.1863	$218.19	$218.20	$218.20
Purchase #4	$103.96	11.821%	$116.2491	$116.25	$116.25	$116.20
Purchase #5	$132.86	9.398%	$145.3462	$145.35	$145.35	$145.30
Purchase #6	$176.51	5.226%	$185.7344	$185.73	$185.75	$185.70
Purchase #7	$209.93	10.308%	$231.5696	$231.57	$231.55	$231.60
7 purchase totals =	$1,239.27		$1,353.0921	$1,353.10	$1,353.10	$1,353.00