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	$46.87	5.174%	$49.2951	$49.30	$49.30	$49.30
Purchase #2	$179.45	12.766%	$202.3586	$202.36	$202.35	$202.40
Purchase #3	$204.79	13.535%	$232.5083	$232.51	$232.50	$232.50
Purchase #4	$101.77	10.214%	$112.1648	$112.16	$112.15	$112.20
Purchase #5	$40.40	12.524%	$45.4597	$45.46	$45.45	$45.50
Purchase #6	$12.57	5.803%	$13.2994	$13.30	$13.30	$13.30
Purchase #7	$53.65	11.591%	$59.8686	$59.87	$59.85	$59.90
7 purchase totals =	$639.50		$714.9545	$714.96	$714.90	$715.10