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	$204.89	13.132%	$231.7962	$231.80	$231.80	$231.80
Purchase #2	$81.73	9.289%	$89.3219	$89.32	$89.30	$89.30
Purchase #3	$100.83	11.847%	$112.7753	$112.78	$112.80	$112.80
Purchase #4	$191.38	5.265%	$201.4562	$201.46	$201.45	$201.50
Purchase #5	$228.98	3.274%	$236.4768	$236.48	$236.50	$236.50
Purchase #6	$195.94	13.739%	$222.8602	$222.86	$222.85	$222.90
Purchase #7	$37.47	4.252%	$39.0632	$39.06	$39.05	$39.10
7 purchase totals =	$1,041.22		$1,133.7498	$1,133.76	$1,133.75	$1,133.90