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	$134.70	6.559%	$143.535	$143.54	$143.55	$143.50
Purchase #2	$180.39	6.312%	$191.7762	$191.78	$191.80	$191.80
Purchase #3	$10.59	13.397%	$12.0087	$12.01	$12.00	$12.00
Purchase #4	$220.84	6.189%	$234.5078	$234.51	$234.50	$234.50
Purchase #5	$49.28	11.718%	$55.0546	$55.05	$55.05	$55.10
Purchase #6	$125.98	12.288%	$141.4604	$141.46	$141.45	$141.50
Purchase #7	$211.90	12.781%	$238.9829	$238.98	$239.00	$239.00
7 purchase totals =	$933.68		$1,017.3256	$1,017.33	$1,017.35	$1,017.40