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	$139.44	13.585%	$158.3829	$158.38	$158.40	$158.40
Purchase #2	$31.89	6.283%	$33.8936	$33.89	$33.90	$33.90
Purchase #3	$121.76	9.850%	$133.7534	$133.75	$133.75	$133.80
Purchase #4	$151.81	11.865%	$169.8223	$169.82	$169.80	$169.80
Purchase #5	$78.54	10.506%	$86.7914	$86.79	$86.80	$86.80
Purchase #6	$145.26	4.278%	$151.4742	$151.47	$151.45	$151.50
Purchase #7	$140.85	8.589%	$152.9476	$152.95	$152.95	$152.90
7 purchase totals =	$809.55		$887.0654	$887.05	$887.05	$887.10