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	$163.61	12.694%	$184.3787	$184.38	$184.40	$184.40
Purchase #2	$136.92	7.834%	$147.6463	$147.65	$147.65	$147.60
Purchase #3	$201.25	5.781%	$212.8843	$212.88	$212.90	$212.90
Purchase #4	$72.35	7.675%	$77.9029	$77.90	$77.90	$77.90
Purchase #5	$107.35	8.788%	$116.7839	$116.78	$116.80	$116.80
Purchase #6	$169.81	9.102%	$185.2661	$185.27	$185.25	$185.30
Purchase #7	$38.43	3.799%	$39.89	$39.89	$39.90	$39.90
7 purchase totals =	$889.72		$964.7522	$964.75	$964.80	$964.80