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	$130.47	5.210%	$137.2675	$137.27	$137.25	$137.30
Purchase #2	$127.37	8.449%	$138.1315	$138.13	$138.15	$138.10
Purchase #3	$99.37	4.142%	$103.4859	$103.49	$103.50	$103.50
Purchase #4	$21.80	12.710%	$24.5708	$24.57	$24.55	$24.60
Purchase #5	$65.46	10.380%	$72.2547	$72.25	$72.25	$72.30
Purchase #6	$182.82	11.111%	$203.1331	$203.13	$203.15	$203.10
Purchase #7	$88.53	7.201%	$94.905	$94.91	$94.90	$94.90
7 purchase totals =	$715.82		$773.7485	$773.75	$773.75	$773.80