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	$89.45	11.352%	$99.6044	$99.60	$99.60	$99.60
Purchase #2	$106.30	12.427%	$119.5099	$119.51	$119.50	$119.50
Purchase #3	$96.99	6.404%	$103.2012	$103.20	$103.20	$103.20
Purchase #4	$97.45	10.199%	$107.3889	$107.39	$107.40	$107.40
Purchase #5	$129.35	12.515%	$145.5382	$145.54	$145.55	$145.50
Purchase #6	$49.34	13.380%	$55.9417	$55.94	$55.95	$55.90
Purchase #7	$45.57	12.484%	$51.259	$51.26	$51.25	$51.30
7 purchase totals =	$614.45		$682.4433	$682.44	$682.45	$682.40