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	$166.78	11.526%	$186.0031	$186.00	$186.00	$186.00
Purchase #2	$38.44	3.801%	$39.9011	$39.90	$39.90	$39.90
Purchase #3	$38.50	13.742%	$43.7907	$43.79	$43.80	$43.80
Purchase #4	$63.38	4.457%	$66.2048	$66.20	$66.20	$66.20
Purchase #5	$151.33	11.177%	$168.2442	$168.24	$168.25	$168.20
Purchase #6	$195.79	6.328%	$208.1796	$208.18	$208.20	$208.20
Purchase #7	$48.33	13.723%	$54.9623	$54.96	$54.95	$55.00
7 purchase totals =	$702.55		$767.2858	$767.27	$767.30	$767.30