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	$38.45	6.343%	$40.8889	$40.89	$40.90	$40.90
Purchase #2	$116.25	13.305%	$131.7171	$131.72	$131.70	$131.70
Purchase #3	$125.33	3.171%	$129.3042	$129.30	$129.30	$129.30
Purchase #4	$142.88	6.694%	$152.4444	$152.44	$152.45	$152.40
Purchase #5	$47.77	10.638%	$52.8518	$52.85	$52.85	$52.90
Purchase #6	$18.87	13.314%	$21.3824	$21.38	$21.40	$21.40
Purchase #7	$240.72	12.567%	$270.9713	$270.97	$270.95	$271.00
7 purchase totals =	$730.27		$799.5601	$799.55	$799.55	$799.60