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	$12.80	8.442%	$13.8806	$13.88	$13.90	$13.90
Purchase #2	$67.79	13.826%	$77.1626	$77.16	$77.15	$77.20
Purchase #3	$90.26	12.411%	$101.4622	$101.46	$101.45	$101.50
Purchase #4	$84.38	4.496%	$88.1737	$88.17	$88.15	$88.20
Purchase #5	$39.81	8.692%	$43.2703	$43.27	$43.25	$43.30
Purchase #6	$38.90	4.214%	$40.5392	$40.54	$40.55	$40.50
Purchase #7	$202.36	11.114%	$224.8503	$224.85	$224.85	$224.90
7 purchase totals =	$536.30		$589.3389	$589.33	$589.30	$589.50