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	$43.79	11.822%	$48.9669	$48.97	$48.95	$49.00
Purchase #2	$67.86	5.382%	$71.5122	$71.51	$71.50	$71.50
Purchase #3	$240.48	11.317%	$267.6951	$267.70	$267.70	$267.70
Purchase #4	$29.51	9.514%	$32.3176	$32.32	$32.30	$32.30
Purchase #5	$109.54	4.827%	$114.8275	$114.83	$114.85	$114.80
Purchase #6	$232.48	7.474%	$249.8556	$249.86	$249.85	$249.90
Purchase #7	$72.83	10.233%	$80.2827	$80.28	$80.30	$80.30
7 purchase totals =	$796.49		$865.4576	$865.47	$865.45	$865.50