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	$140.89	4.589%	$147.3554	$147.36	$147.35	$147.40
Purchase #2	$47.88	11.562%	$53.4159	$53.42	$53.40	$53.40
Purchase #3	$172.48	11.489%	$192.2962	$192.30	$192.30	$192.30
Purchase #4	$82.78	13.389%	$93.8634	$93.86	$93.85	$93.90
Purchase #5	$59.35	12.510%	$66.7747	$66.77	$66.75	$66.80
Purchase #6	$21.84	13.807%	$24.8554	$24.86	$24.85	$24.90
Purchase #7	$124.25	5.453%	$131.0254	$131.03	$131.05	$131.00
7 purchase totals =	$649.47		$709.5864	$709.60	$709.55	$709.70