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	$71.86	11.436%	$80.0779	$80.08	$80.10	$80.10
Purchase #2	$67.35	6.380%	$71.6469	$71.65	$71.65	$71.60
Purchase #3	$201.30	9.158%	$219.7351	$219.74	$219.75	$219.70
Purchase #4	$103.86	7.135%	$111.2704	$111.27	$111.25	$111.30
Purchase #5	$10.51	6.302%	$11.1723	$11.17	$11.15	$11.20
Purchase #6	$204.57	8.183%	$221.31	$221.31	$221.30	$221.30
Purchase #7	$134.83	5.848%	$142.7149	$142.71	$142.70	$142.70
7 purchase totals =	$794.28		$857.9275	$857.93	$857.90	$857.90