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	$192.31	3.226%	$198.5139	$198.51	$198.50	$198.50
Purchase #2	$115.32	4.432%	$120.431	$120.43	$120.45	$120.40
Purchase #3	$103.49	10.670%	$114.5324	$114.53	$114.55	$114.50
Purchase #4	$36.93	9.707%	$40.5148	$40.51	$40.50	$40.50
Purchase #5	$146.74	10.638%	$162.3502	$162.35	$162.35	$162.40
Purchase #6	$80.74	10.200%	$88.9755	$88.98	$89.00	$89.00
Purchase #7	$103.51	8.791%	$112.6096	$112.61	$112.60	$112.60
7 purchase totals =	$779.04		$837.9274	$837.92	$837.95	$837.90