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	$37.53	13.849%	$42.7275	$42.73	$42.75	$42.70
Purchase #2	$94.71	5.683%	$100.0924	$100.09	$100.10	$100.10
Purchase #3	$240.45	12.170%	$269.7128	$269.71	$269.70	$269.70
Purchase #4	$125.94	5.773%	$133.2105	$133.21	$133.20	$133.20
Purchase #5	$19.59	5.354%	$20.6388	$20.64	$20.65	$20.60
Purchase #6	$132.66	8.424%	$143.8353	$143.84	$143.85	$143.80
Purchase #7	$50.86	13.804%	$57.8807	$57.88	$57.90	$57.90
7 purchase totals =	$701.74		$768.0980	$768.10	$768.15	$768.00