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	$166.52	13.255%	$188.5922	$188.59	$188.60	$188.60
Purchase #2	$106.55	3.181%	$109.9394	$109.94	$109.95	$109.90
Purchase #3	$80.83	7.257%	$86.6958	$86.70	$86.70	$86.70
Purchase #4	$59.55	13.137%	$67.3731	$67.37	$67.35	$67.40
Purchase #5	$126.79	11.437%	$141.291	$141.29	$141.30	$141.30
Purchase #6	$67.49	7.793%	$72.7495	$72.75	$72.75	$72.70
Purchase #7	$113.29	9.211%	$123.7251	$123.73	$123.75	$123.70
7 purchase totals =	$721.02		$790.3661	$790.37	$790.40	$790.30