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	$161.89	4.377%	$168.9759	$168.98	$169.00	$169.00
Purchase #2	$21.99	12.238%	$24.6811	$24.68	$24.70	$24.70
Purchase #3	$79.93	12.216%	$89.6942	$89.69	$89.70	$89.70
Purchase #4	$46.70	4.807%	$48.9449	$48.94	$48.95	$48.90
Purchase #5	$89.45	6.626%	$95.377	$95.38	$95.40	$95.40
Purchase #6	$109.28	9.362%	$119.5108	$119.51	$119.50	$119.50
Purchase #7	$82.94	13.412%	$94.0639	$94.06	$94.05	$94.10
7 purchase totals =	$592.18		$641.2478	$641.24	$641.30	$641.30