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	$144.95	9.540%	$158.7782	$158.78	$158.80	$158.80
Purchase #2	$91.30	12.614%	$102.8166	$102.82	$102.80	$102.80
Purchase #3	$94.93	3.234%	$98	$98.00	$98.00	$98.00
Purchase #4	$156.68	7.609%	$168.6018	$168.60	$168.60	$168.60
Purchase #5	$150.70	10.546%	$166.5928	$166.59	$166.60	$166.60
Purchase #6	$33.86	7.527%	$36.4086	$36.41	$36.40	$36.40
Purchase #7	$19.71	9.711%	$21.624	$21.62	$21.60	$21.60
7 purchase totals =	$692.13		$752.8220	$752.82	$752.80	$752.80