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	$19.37	11.114%	$21.5228	$21.52	$21.50	$21.50
Purchase #2	$104.78	8.317%	$113.4946	$113.49	$113.50	$113.50
Purchase #3	$19.77	7.278%	$21.2089	$21.21	$21.20	$21.20
Purchase #4	$120.77	7.677%	$130.0415	$130.04	$130.05	$130.00
Purchase #5	$57.34	3.629%	$59.4209	$59.42	$59.40	$59.40
Purchase #6	$168.55	9.496%	$184.5555	$184.56	$184.55	$184.60
Purchase #7	$61.55	8.216%	$66.6069	$66.61	$66.60	$66.60
7 purchase totals =	$552.13		$596.8511	$596.85	$596.80	$596.80