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	$169.33	6.528%	$180.3839	$180.38	$180.40	$180.40
Purchase #2	$159.45	8.546%	$173.0766	$173.08	$173.10	$173.10
Purchase #3	$62.33	13.737%	$70.8923	$70.89	$70.90	$70.90
Purchase #4	$6.97	12.156%	$7.8173	$7.82	$7.80	$7.80
Purchase #5	$164.49	9.373%	$179.9076	$179.91	$179.90	$179.90
Purchase #6	$185.93	10.193%	$204.8818	$204.88	$204.90	$204.90
Purchase #7	$55.91	7.130%	$59.8964	$59.90	$59.90	$59.90
7 purchase totals =	$804.41		$876.8559	$876.86	$876.90	$876.90