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	$233.30	9.674%	$255.8694	$255.87	$255.85	$255.90
Purchase #2	$56.27	8.184%	$60.8751	$60.88	$60.90	$60.90
Purchase #3	$170.40	8.172%	$184.3251	$184.33	$184.35	$184.30
Purchase #4	$49.80	5.168%	$52.3737	$52.37	$52.35	$52.40
Purchase #5	$158.64	6.534%	$169.0055	$169.01	$169.00	$169.00
Purchase #6	$162.82	10.250%	$179.5091	$179.51	$179.50	$179.50
Purchase #7	$167.74	11.822%	$187.5702	$187.57	$187.55	$187.60
7 purchase totals =	$998.97		$1,089.5281	$1,089.54	$1,089.50	$1,089.60