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	$231.43	10.567%	$255.8852	$255.89	$255.90	$255.90
Purchase #2	$38.85	11.454%	$43.2999	$43.30	$43.30	$43.30
Purchase #3	$54.83	3.102%	$56.5308	$56.53	$56.55	$56.50
Purchase #4	$84.50	10.710%	$93.55	$93.55	$93.55	$93.60
Purchase #5	$37.98	7.770%	$40.931	$40.93	$40.95	$40.90
Purchase #6	$35.30	10.728%	$39.087	$39.09	$39.10	$39.10
Purchase #7	$239.41	4.309%	$249.7262	$249.73	$249.75	$249.70
7 purchase totals =	$722.30		$779.0101	$779.02	$779.10	$779.00