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	$91.99	9.463%	$100.695	$100.70	$100.70	$100.70
Purchase #2	$76.64	8.420%	$83.0931	$83.09	$83.10	$83.10
Purchase #3	$170.71	8.571%	$185.3416	$185.34	$185.35	$185.30
Purchase #4	$46.86	5.600%	$49.4842	$49.48	$49.50	$49.50
Purchase #5	$195.27	11.240%	$217.2183	$217.22	$217.20	$217.20
Purchase #6	$171.89	7.214%	$184.2901	$184.29	$184.30	$184.30
Purchase #7	$59.67	10.238%	$65.779	$65.78	$65.80	$65.80
7 purchase totals =	$813.03		$885.9013	$885.90	$885.95	$885.90