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	$72.48	12.629%	$81.6335	$81.63	$81.65	$81.60
Purchase #2	$214.91	13.673%	$244.2946	$244.29	$244.30	$244.30
Purchase #3	$197.73	5.643%	$208.8879	$208.89	$208.90	$208.90
Purchase #4	$45.82	5.579%	$48.3763	$48.38	$48.40	$48.40
Purchase #5	$213.51	12.639%	$240.4955	$240.50	$240.50	$240.50
Purchase #6	$67.48	7.765%	$72.7198	$72.72	$72.70	$72.70
Purchase #7	$96.88	6.393%	$103.0735	$103.07	$103.05	$103.10
7 purchase totals =	$908.81		$999.4811	$999.48	$999.50	$999.50