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	$234.90	9.599%	$257.4481	$257.45	$257.45	$257.40
Purchase #2	$162.32	3.789%	$168.4703	$168.47	$168.45	$168.50
Purchase #3	$52.79	3.864%	$54.8298	$54.83	$54.85	$54.80
Purchase #4	$179.51	9.208%	$196.0393	$196.04	$196.05	$196.00
Purchase #5	$242.31	3.686%	$251.2415	$251.24	$251.25	$251.20
Purchase #6	$26.90	7.340%	$28.8745	$28.87	$28.85	$28.90
Purchase #7	$26.97	5.338%	$28.4097	$28.41	$28.40	$28.40
7 purchase totals =	$925.70		$985.3132	$985.31	$985.30	$985.20