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	$150.32	11.285%	$167.2836	$167.28	$167.30	$167.30
Purchase #2	$66.71	8.721%	$72.5278	$72.53	$72.55	$72.50
Purchase #3	$109.67	4.412%	$114.5086	$114.51	$114.50	$114.50
Purchase #4	$183.94	3.248%	$189.9144	$189.91	$189.90	$189.90
Purchase #5	$68.25	7.157%	$73.1347	$73.13	$73.15	$73.10
Purchase #6	$178.69	4.331%	$186.4291	$186.43	$186.45	$186.40
Purchase #7	$95.43	10.318%	$105.2765	$105.28	$105.30	$105.30
7 purchase totals =	$853.01		$909.0747	$909.07	$909.15	$909.00