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	$226.85	7.395%	$243.6256	$243.63	$243.65	$243.60
Purchase #2	$38.97	3.216%	$40.2233	$40.22	$40.20	$40.20
Purchase #3	$151.95	8.515%	$164.8885	$164.89	$164.90	$164.90
Purchase #4	$132.83	10.282%	$146.4876	$146.49	$146.50	$146.50
Purchase #5	$14.90	5.474%	$15.7156	$15.72	$15.70	$15.70
Purchase #6	$213.32	4.435%	$222.7807	$222.78	$222.80	$222.80
Purchase #7	$100.85	8.174%	$109.0935	$109.09	$109.10	$109.10
7 purchase totals =	$879.67		$942.8148	$942.82	$942.85	$942.80