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	$50.46	5.571%	$53.2711	$53.27	$53.25	$53.30
Purchase #2	$125.42	10.801%	$138.9666	$138.97	$138.95	$139.00
Purchase #3	$125.83	3.819%	$130.6354	$130.64	$130.65	$130.60
Purchase #4	$237.97	8.843%	$259.0137	$259.01	$259.00	$259.00
Purchase #5	$80.88	10.690%	$89.5261	$89.53	$89.55	$89.50
Purchase #6	$179.53	10.409%	$198.2173	$198.22	$198.20	$198.20
Purchase #7	$195.73	11.323%	$217.8925	$217.89	$217.90	$217.90
7 purchase totals =	$995.82		$1,087.5227	$1,087.53	$1,087.50	$1,087.50