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	$131.89	8.143%	$142.6298	$142.63	$142.65	$142.60
Purchase #2	$110.29	3.316%	$113.9472	$113.95	$113.95	$113.90
Purchase #3	$99.80	10.716%	$110.4946	$110.49	$110.50	$110.50
Purchase #4	$25.63	5.422%	$27.0197	$27.02	$27.00	$27.00
Purchase #5	$230.33	12.640%	$259.4437	$259.44	$259.45	$259.40
Purchase #6	$32.34	3.185%	$33.37	$33.37	$33.35	$33.40
Purchase #7	$139.90	3.265%	$144.4677	$144.47	$144.45	$144.50
7 purchase totals =	$770.18		$831.3727	$831.37	$831.35	$831.30