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	$40.31	7.342%	$43.2696	$43.27	$43.25	$43.30
Purchase #2	$135.73	4.718%	$142.1337	$142.13	$142.15	$142.10
Purchase #3	$250.63	6.496%	$266.9109	$266.91	$266.90	$266.90
Purchase #4	$133.27	4.103%	$138.7381	$138.74	$138.75	$138.70
Purchase #5	$127.73	3.303%	$131.9489	$131.95	$131.95	$131.90
Purchase #6	$163.78	4.573%	$171.2697	$171.27	$171.25	$171.30
Purchase #7	$7.96	6.240%	$8.4567	$8.46	$8.45	$8.50
7 purchase totals =	$859.41		$902.7276	$902.73	$902.70	$902.70