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	$232.82	9.658%	$255.3058	$255.31	$255.30	$255.30
Purchase #2	$127.76	6.738%	$136.3685	$136.37	$136.35	$136.40
Purchase #3	$35.98	13.329%	$40.7758	$40.78	$40.80	$40.80
Purchase #4	$242.59	8.479%	$263.1592	$263.16	$263.15	$263.20
Purchase #5	$132.68	8.482%	$143.9339	$143.93	$143.95	$143.90
Purchase #6	$209.34	7.128%	$224.2618	$224.26	$224.25	$224.30
Purchase #7	$114.27	3.649%	$118.4397	$118.44	$118.45	$118.40
7 purchase totals =	$1,095.44		$1,182.2447	$1,182.25	$1,182.25	$1,182.30