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	$48.48	5.190%	$50.9961	$51.00	$51.00	$51.00
Purchase #2	$60.37	11.440%	$67.2763	$67.28	$67.30	$67.30
Purchase #3	$136.76	10.715%	$151.4138	$151.41	$151.40	$151.40
Purchase #4	$63.35	7.151%	$67.8802	$67.88	$67.90	$67.90
Purchase #5	$56.45	7.232%	$60.5325	$60.53	$60.55	$60.50
Purchase #6	$75.38	4.552%	$78.8113	$78.81	$78.80	$78.80
Purchase #7	$136.25	3.421%	$140.9111	$140.91	$140.90	$140.90
7 purchase totals =	$577.04		$617.8213	$617.82	$617.85	$617.80