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	$240.86	11.489%	$268.5324	$268.53	$268.55	$268.50
Purchase #2	$65.94	8.730%	$71.6966	$71.70	$71.70	$71.70
Purchase #3	$106.29	11.848%	$118.8832	$118.88	$118.90	$118.90
Purchase #4	$176.87	10.498%	$195.4378	$195.44	$195.45	$195.40
Purchase #5	$54.59	5.548%	$57.6187	$57.62	$57.60	$57.60
Purchase #6	$105.67	3.640%	$109.5164	$109.52	$109.50	$109.50
Purchase #7	$11.79	10.870%	$13.0716	$13.07	$13.05	$13.10
7 purchase totals =	$762.01		$834.7567	$834.76	$834.75	$834.70