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	$170.81	5.687%	$180.524	$180.52	$180.50	$180.50
Purchase #2	$42.78	5.361%	$45.0734	$45.07	$45.05	$45.10
Purchase #3	$70.71	13.615%	$80.3372	$80.34	$80.35	$80.30
Purchase #4	$68.70	5.317%	$72.3528	$72.35	$72.35	$72.40
Purchase #5	$241.67	3.608%	$250.3895	$250.39	$250.40	$250.40
Purchase #6	$248.89	5.741%	$263.1788	$263.18	$263.20	$263.20
Purchase #7	$231.64	3.278%	$239.2332	$239.23	$239.25	$239.20
7 purchase totals =	$1,075.20		$1,131.0889	$1,131.08	$1,131.10	$1,131.10