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	$138.36	6.356%	$147.1542	$147.15	$147.15	$147.20
Purchase #2	$77.51	3.142%	$79.9454	$79.95	$79.95	$79.90
Purchase #3	$27.31	9.457%	$29.8927	$29.89	$29.90	$29.90
Purchase #4	$91.83	12.615%	$103.4144	$103.41	$103.40	$103.40
Purchase #5	$64.83	10.725%	$71.783	$71.78	$71.80	$71.80
Purchase #6	$123.37	6.474%	$131.357	$131.36	$131.35	$131.40
Purchase #7	$105.93	10.561%	$117.1173	$117.12	$117.10	$117.10
7 purchase totals =	$629.14		$680.6640	$680.66	$680.65	$680.70