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	$150.58	11.859%	$168.4373	$168.44	$168.45	$168.40
Purchase #2	$237.88	4.677%	$249.0056	$249.01	$249.00	$249.00
Purchase #3	$248.46	11.690%	$277.505	$277.51	$277.50	$277.50
Purchase #4	$51.32	6.719%	$54.7682	$54.77	$54.75	$54.80
Purchase #5	$131.47	8.647%	$142.8382	$142.84	$142.85	$142.80
Purchase #6	$220.56	4.746%	$231.0278	$231.03	$231.05	$231.00
Purchase #7	$243.78	5.164%	$256.3688	$256.37	$256.35	$256.40
7 purchase totals =	$1,284.05		$1,379.9509	$1,379.97	$1,379.95	$1,379.90