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	$38.36	11.521%	$42.7795	$42.78	$42.80	$42.80
Purchase #2	$163.45	6.461%	$174.0105	$174.01	$174.00	$174.00
Purchase #3	$38.54	12.174%	$43.2319	$43.23	$43.25	$43.20
Purchase #4	$234.74	6.513%	$250.0286	$250.03	$250.05	$250.00
Purchase #5	$104.72	9.764%	$114.9449	$114.94	$114.95	$114.90
Purchase #6	$68.67	5.708%	$72.5897	$72.59	$72.60	$72.60
Purchase #7	$133.97	3.709%	$138.9389	$138.94	$138.95	$138.90
7 purchase totals =	$782.45		$836.5240	$836.52	$836.60	$836.40