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	$211.66	3.224%	$218.4839	$218.48	$218.50	$218.50
Purchase #2	$156.27	3.147%	$161.1878	$161.19	$161.20	$161.20
Purchase #3	$139.66	8.316%	$151.2741	$151.27	$151.25	$151.30
Purchase #4	$171.60	8.202%	$185.6746	$185.67	$185.65	$185.70
Purchase #5	$16.39	12.165%	$18.3838	$18.38	$18.40	$18.40
Purchase #6	$47.32	4.818%	$49.5999	$49.60	$49.60	$49.60
Purchase #7	$247.48	3.390%	$255.8696	$255.87	$255.85	$255.90
7 purchase totals =	$990.38		$1,040.4737	$1,040.46	$1,040.45	$1,040.60