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	$123.72	11.486%	$137.9305	$137.93	$137.95	$137.90
Purchase #2	$181.44	4.191%	$189.0442	$189.04	$189.05	$189.00
Purchase #3	$51.48	6.759%	$54.9595	$54.96	$54.95	$55.00
Purchase #4	$72.69	10.420%	$80.2643	$80.26	$80.25	$80.30
Purchase #5	$39.86	9.358%	$43.5901	$43.59	$43.60	$43.60
Purchase #6	$17.78	11.807%	$19.8793	$19.88	$19.90	$19.90
Purchase #7	$100.29	3.657%	$103.9576	$103.96	$103.95	$104.00
7 purchase totals =	$587.26		$629.6255	$629.62	$629.65	$629.70